Adding RAM to the amount already in your Mac is a must, I would think. So as soon as you can, add some.
For now, you could also download
MainMenu and use it to run your Maintenance tasks on a daily, weekly and monthly basis if you don't let your Mac on all the time.
Till you get the extra RAM, to spruce up the performance a little I would use MainMenu to clear all the caches: users, browsers, system, etc. That usually helps a little.
As for the
Repairing Disk Permissions thing, if you are running Mac OS X Tiger 10.4.x (which I assume you are using) it isn't as needed as it was with Mac OS X Panther (10.3.x). The messed up disk permissions thing has been pretty much fixed now.
You can always go through that process if you want, but unless you have been really
active in
playing around with your Mac OS X install, there shouldn't be much permission repairs.