It's today's woot.

Nobody is really looking at skinny/flabby geeks. They are all looking at the hot chicks. The most serious people at the gym (the ones getting the results) are introverts too, at least for those few hours each week, and would prefer to be left alone while they train.

7 or 8 years ago when I was in your position (self conscious about exercising) I decided that it was time to do something about my physical state. I found a gym that was affiliated with our local university hospital system (it was the cleanest of the 3 or 4 I looked at in my price range). I made an appointment with a trainer, learned a few exercises, and then began to go during off hours. I consider the gym membership to be one of my most worthwhile expenditures. Having that membership is encouragement to go, and gets me access to equipment that might not otherwise be available (e.g. power rack, a shitload of plates, dumbbells in a much wider range than practical for home, and so on.)

Once you have pushed yourself into a routine, make a point of lifting heavy weights and eating real food (100 calories portions of junk food are still 100 calories of crap). Go easy at first. After a few months, switch said routine (google WSFSB). Don't be intimidated by new exercises and barbells and assorted machines. Watch other people, and if you have to, ask a staff member for instruction. Stick to compound exercises. The thigh abductor/adductor machine is for chicks wearing spandex.

Finally, go have a look at t-nation.com. Skip the forums and just read the articles for now. Get a thicker skin if you are going to read the forums.

The progress that comes with even just 6 months of decent gym time will absolutely change your life for the better. (Yes, you have to keep going.) Read up, lift heavy, eat real food, improve physique, become more self confident.