i have a 4gb pen drive but my home desktop has 512mb ram so how can i use my pen drive to increase my ram?
please do help me.

yeah you can use ur pendrive as ram..

If you have Windows Vista or above then you can use it via ReadytoBoost feature. If you have XP then use eboostr Software.

But as discussed already, it will not help much, better increase your RAM to get real improvement.

PS: I just removed duplicate post, please ask a question only once, it will help to get asnwer quicker.