Great advice in here. I won't bore you with my drivel, as it would pretty much echo everything here!
Suffice to say, get a cheap used bike and take baby steps. If it breaks, buy another!

You'll soon find out how much you like being back on the bike, and I'm sure you'll like it! I've lost about 25 lbs (240 to 215) over the past 6 months, mainly attributable to cycling and a 'lifestyle change' towards eating.
Darn it... I ended up drivelling anyway...