First, what is the landscape like that you will be commuting over? A lot of hills? Or mostly flat? This makes a HUGE difference when buying a bike.
No matter what, get a bike with fenders and a rack. You'll need the fenders to keep crud off of you, your stuff and your drivetrain. Then you'll need a rack to carry your laptop and effects.
For carrying your laptop, I would highly suggest getting a separate laptop sleeve that is well-padded. Next, you can get a pannier to put it in or anothe bag and strap it down very well. You'll want to make sure the laptop doesn't knock around so get a pannier/bag that's snug or simply fill up the pannier/bag with things like your clothes, lunch, etc.
As for limited funds, know how much you can spend on a bike including accessories like a helmet, lights, rack, bag(s), etc. Next, I would suggest that you look into buying a solid USED bike. Check local listings on Craigslist. Also, thrift stores and yard sales are nice to check out too. Lastly, you can take a look at eBay just make sure you know what you're buying.
Last edited by KitN; 07-24-09 at 05:14 PM.