You can "test" it by going to a lbs (local bike shop) and seeing if you can borrow a bike for a day... or rent it. do the ride, see how you feel. When I started to ride, a 4 mile ride to a friend's house nearly killed me, I thought I'd die in his front yard, now 40-50 mile rides on the weekend are the norm.
Avoid that bike and most folding bikes for commuting unless you need to take them on a subway. They are heavy, cost too much and usually have specific parts to them that are hard and spendy to replace.
5-10 minutes by car, depending on traffic lights could be 4-12 miles, not sure how fast you drive. My car commute to work is 8 miles and takes 12 minutes on a good day with light to average traffic. I go a different route (not via highway obviously) on my bike and it's 7.15 miles, when I started to commute it was 28-29 minutes, now I'm in the 25-26 minute bracket because I'm in better shape, weigh almost 30 pounds less and have built leg muscles.
Laptop issues. Yes, it's possible. They make panniers and covers for them that are waterproof, as well as backpacks and messenger bags (r.e. load bags for example) that will keep your stuff dry, and they make waterproof covers for most backpacks as well. If you are real nervous, large ziplock bag wouldn't hurt the lappy.
Rain in general, I watch my local doplar radar pretty close and avoid rain or the chance of rain whenever I can. I've yet to get caught in it while commuting, but have been caught while out on fun rides. It sucks, I'm not going to lie, but you can only get so wet. If you are going to become a regular commuter by bike, you will get caught in it sooner or later. Cheap rain jackets that will fit in your bag are a good start. Grin and bear it, especially if it's a short ride. One commuter I know who hasn't driven to work in over 10 years will ride 2ish miles to a local bus stop if it's raining really hard, take the bus 9/10ths of the way to work and ride the last mile from the bus stop to his job. That cuts down on the wet time.
Stairs aren't that big of a deal, honestly. A modern road bicycle weights 21-23lbs... if you went with a single speed or fixed gear it might only be 16-18lbs. I carry my bike out of my condo down a half flight of stairs, which are uber long, 2-step stairs, not a big deal.
Dirt / mud, I ride a road bicycle, so I dont' cut corners through yards or on bike trails and outside of a puddle or getting caught in the rain, there's no mud getting trecked inside my house. Every few weeks I wipe my bike down so it stays pretty clean.
Clothing. This is where you will be able to answer what is best for you. Some commuters will take a week's worth of clothing in on Monday (via bike or car) and then bring home the dirty as they see fit. Others work in their commuting clothing, depending on profession. Personally, I keep a pair of jeans and sneakers at work and only carry polo shirts, boxers and under shirts with me daily, taking the jeans home every few days to exchange with others, as I'm in a pretty casual work place.
This thread is about biking to work, not replacing your car with a bike... so yes, you probably will have to keep your car, I do because I take my dog places, and drive to places to ride from time to time.
Is it even worth it to own a bike? That's a really loaded question. My opinon, yes, yes it is. I've lost nearly 30 pounds in the last 2.5 months, helped to save the enviornment, saved $40 / year on my car insurance and saved gas money. Now, there is an initial investment. I got a left over bike so I saved a good deal of money right there, long story short I ended up paying $400 for a $550 bike. Now, I also have about $250 worth of extras to the bike, like shoes, clipless pedals, helmet, floor pump, saddle bag, etc. etc. plus another $100-150 in cycling specific clothing, so out of pocket I've spent about $800. Take a look at this article I wrote to get an idea of how much money I save riding to work vs. driving [my 35mpg civic] http://www.randomn3ss.com/2008/10/06/ri ... uncle-sam/
So for arguments sake, it costs $30 to fill my civic, which gets 350 miles per tank (rounding numbers for easy math). I'd have to ride my bike about 27 fill-ups worth of gas, or just under 9,500 total miles. That doesn't include things like tube and tire replacement, wheels being trued or other costs of ownership. OK, that's a bit excessive, but look at the bigger picture. I saved $40 / year by calling my insurance company and having my auto insurance switched to "pleasure vehicle" instead of "commuting vehicle" - that is more than a tank of gas and knocks about 450-500 miles off that 9,500 mile total right there. If I cancled my gym membership (I'm not, but let's say I did), I'd save about another $250 / year because I do get a great workout in by riding nearly an hour a day (back and forth to work). I'm keeping it because the winter is almost here and my weekend fun rides are almost gone. If I canceled that I'd knock my initial investment of $800 in bike, accessories and clothing down to a modest $510. If my employer decides that it will give me the $20 tax free credit monthly for commuting, I'll get another $240 / year back, meaning the true cost of my investment is only about $270. That's about 9 tank-fulls of gas, just over 3,000 miles.
That's the first I've broken down the cost of ownership for me, your results may vary and my math may be off a bit here and there.
As for making the leap, read the http://commutebybike.com/
site I linked to earlier, avoid that Strida bike and get a real commuting bike based on your needs, go and talk to a local bike shop (or more than one if they are close) and tell him what you want to accomplish, what your budget is and how often you plan, they will help get you in the right setup, and start riding. If you hate it, sell the bike on craigslist - used bicycles tend to hold a good portion of their value.
I'm currently looking into getting a light or two so I can ride in the evenings now that the sun is setting around 6pm here, it just seems silly for me to drive 2 miles to my gym so I can get on a treadmill and run, when I could just ride my bike. I'll follow this thread via email so if you have more questions I can try to get you answers.