Hello sraghav,
FightAIDS@Home takes about 300 MB of Virtual Memory. I am unfamiliar with Ad-Watch. HPF takes about 200 MB of Virtual Memory.

I suppose the first thing to ask is about your Virtual Memory setting. You can find this (for Windows XP) at Start - Settings - Control Panel - System.
Select Advanced, then in the Performance section select Settings. Select Advanced again. Then look in the Virtual Memory section and select Change. Be cautious here. It does not show you your virtual memory settings unntil you select Change. Now you can see what you have. There are some warnings that I could give here. It is never a bad idea to select Cancel and ask for advice at this point.

So - - do you allow the OS to manage Virtual Memory or do you have a fixed size? And what is the symptom that tells you that Ad-Watch is grabbing lots of Virtual Memory.

mycrofth