Vista has a feature called ReadyBoost to use an external memory device as a system memory of the PC. No need to say that if the system memory is higher, your PC processing will become faster.
For making the flash drive work as system memory, follow the below steps:
1- Insert the flash drive into the USB port.
2- Go to the “My Computer” window.
3- Right Click on the Flash Drive directory “Removable Disk”
4- Go to the properties section of the flash drive
5- Click on the ReadyBoost tab
6- Check the option “Use this device” and allocate the memory or space which you want to use as a system memory (i.e. RAM) in your PC
That’s it. You can see the change in your system performance especially when you are opening a big application.