The ReadyBoost feature in Windows 7 is an easy way to speed up your PC; it works by using any kind of high speed portable flash mass storage system as a cache (for example a memory stick or SD Card.) It is not the same as adding more physical RAM to your PC but can make an improvement to the overall speed of it. Please note that the media needs to be high speed with an access time of 1 ms or less.
To set it up, simply insert the mass storage device. This should bring up the autoplay window and from here you can select speed up my system.
In the options screen you can choose to dedicate the device for use with ReadyBoost or you can specify how much space to use.
Once done ReadyBoost will automatically configure the cache for you.
To stop using ReadyBoost you can simply remove the device from your PC.