Use your Hard drive as RAM.

Actually this feature was given in fedora 10(my recent OS). During installation itself it will ask for the size of hard disk space to use as RAM. Just by entering a value which is double the size of your physical RAM does the job.So if you already have a 512 Mb RAM, Now your Linux OS will be running with 1GB RAM.This technique seem to have great effect on my sluggish computer.I even heard that it is possible to use Pen drive as RAM in vista or something.Not a bad one though!!