Your symptoms are very different from mine, but I have a Macbook Pro which had a failing fan. In my case, it was the fans that cooled the CPU. My machine would occasionally freeze up, or just certain processes would freeze up, as the processor would hit a critical temperature and then stop processing to prevent overheating. Besides that, the fans made noises like dying jet engines.
A hardware test confirmed that it was the fans, so I took it in to a Genius Bar. This was a smaller Apple store inside a mall, and they didn't have the fans in stock.
The tech then gave me three options: (1) leave the machine there, they would get the part in a few days and I could pick it up, (2) they would ship it to the nearest service depot and mail it straight from the depot back to me, or (3) they would order the part, call me when it came in, and I could then just schedule two consecutive appointments to give them the hour (half-hour?) they need to fix it and give it right back. Apple is REALLY helpful in trying to minimize the turn-around time if it's a major problem like that.
In my case, I chose option (2), since I didn't have a car at the time and I didn't want to have to find another ride to the store. I don't know which would really be best for you- in your case, your machine seems virtually unusable, so the tech will probably be able to recommend which option gives the best turnaround time. If they have the part, it'll be quick- my only worry is if something else might be going wrong, which might take additional time and maybe need other parts.
Good luck, and in the meantime- BACK UP EVERYTHING, if at all possible. Do you have a walk-in refrigerator handy?
