My hard drive is 5400rpm and works fine so dont worry if yours is the same.

Another thing you can try is making sure you have the latest drivers, I had loads of problems till I updated the drivers for my soundcard so try that. I have 256ddr too so I dont see how adding more ram would make any real change to your situation, a defrag and test should do, use a program like norton systemworks to optimize, tweak and fix the registry.