Before you rush out and purchase some RAM just try a few of these.
1st Right click on My Computer - Click on Properties @ the bottom - Click on the Advanced tab - in the Performance box click on the Settings tab - now click on Advanced again, now at the bottom you will see Virtual Memory click on Change Make sure you put a tick in the Custom size and put this amount in each box Initial size (mb) 384 Maximum size 384 (mb) click on set - ok then Apply then ok again.
This will ask you to reboot your pc so do so.
Next I know most ppl like to have a Screen saver but even these use System Memory, on your pc. Right click anywhere on your desktop click properties. Click on Screen saver and set it to none. Do the same with the Desktop.
Now 1 more thing to try after doing this you should see a little speed increase with your pc. Right click on my computer click on properties - click on Advanced in the performance box click on settings. Now where it says Adjust for best performance tick that click on Apply then ok. Your screen will go a crappy grey colour but this should give you more RAM and a little speed increase.