Hey folks. I have a MacBook Pro 17 inches (early 2009) with 2.8 GHz C2D and 4GB RAM on it. My OS is 10.6.4 and have all the latest updates installed.**I have used this computer for 10 months and now it becomes so slow. I did all the stuffs that may help to speed it up(repair disk permission, repair disk, uninstall unnecessary softwares, only one user account, get rid of startup items), but none of them seems to work. I even went to the genius bar, but the genius there said there is nothing they can do. They suggested me to upgrade the memory to 8 gig. It will cost me at least 300 bucks to do that! Don't want to invest that much on a old MacBook Pro. But the thing is, I have a lot of friends using MacBook that has only 1 or 2 gig memory but their computers are still way faster than mine. They can open a lot of programs at the same time but I cannot. If I do, the computer gonna be really sluggish, and sometimes crash. I also don't think it is the problem of the free space on my hard drive since I have a 500GB hard drive and 80GB free space on it.
Can anyone help me to figure out some possible reasons for my slow Mac? And some tips for me to speed it up? I have already tried to reinstall the system and restore it using time machine backup, but it didn't help too much. Thank you!*

Can anyone help me to figure out some possible reasons for my slow Mac? And some tips for me to speed it up? I have already tried to reinstall the system and restore it using time machine backup, but it didn't help too much. Thank you!*