My bike doesn't work

Technically it was my grandpa's bike, and after that my brother had it for a while, but it's mine now. Anyway, being here in Boulder it has suddenly become very important to have a working bike, especially since I don't have the money to buy a bus pass, many things are too far (and hot) to walk to, and gas is far too expensive to waste on all the little errands one must do up here. Needless to say, having a bike that works has suddenly jumped up on my list and, unfortunately, it is not yet accomplished. I discovered two days in here that the seat was way too high, so I had to wait for dad to come down and help me with that. Then it took another day to actually try and ride the thing, only to find out that something is really wrong with the way the chain is riding. No matter how I adjust the speed handles, or don't, the chain keeps jumping rails. Riding down a single block it jumps maybe a dozen times to different speeds. One second it's normal, the next it's super easy, then suddenly it's almost too hard to pedal. I'm told that it probably needs tuning at the shop or some such, which I don't even have $15-20 right now to do even that much. Thankfully my parents will help me out with that too.

On a side note, I'm rather annoyed that my previous job always payed us the very last day of the month, as my last paycheck comes at the end of this month, but rent here needs to be payed the very next day, and not by me, but by another guy in the house, who I have to get the money to before then. Blech.