This steps good for who has slow PC running Windows XP. For good performance Win XP need 256mb of RAM or more. So if you have less than 256mb, better try this. This is step by step how to make pendrive as a RAM.
1. Plug in empty pendrive
2. Let the PC do what ever its want to do
3. After finish, right click on My Computer
4. Goto Properties > Advanced > Performance Settings
5. Advanced > Change
6. Select your pendrive & click on Custom Size
7. Enter the same amount in the Initial and the Max columns
Now you just used the space of the PenDrive as a Virtual Memory for your computer. I suggest you to used 1GB pendrive or 2GB pendrive or more big size in step 1. Good luck >>:)
p/s: for the best result, please used hi-speed rate transfer pendrive.