you have at least 2GB of RAM in that model so if you are really only running safari it shouldn't be an issue, but to find out how much ram you have click on the apple logo on the top left of the screen and then click on about this mac which will bring up a window with some info about your computer including the amount of memory I attached a screen shot of the window from my computer so you can see what it looks like the ammount of RAM you have is listed next to where it says memory so in my example here you can see that I have 2GB of RAM.
Another thing you could try is resetting Safari, go to the safari menu and click "reset Safari" you could also go to disk utility and repair permissions. one other thing that could be slowing your computer down is if you have too much stuff on your desktop, try to organize that and put it in a folder somewhere else.