|dont buy a DELL ;-)|
open msconfig and stop all startup programs you dont use, stop all process you dont use, get more memory, remove all programs you dont use.
run from power as much as possible, defrag the hard drive, clean up the hard drive.
thats about as far you can go, do not use any third party registry cleaners, douse so called third party anti virus/firewalls, win 7 defender/firewall and security essentials is sufficient for most people.
get rid all the dell crap, use sumatra pdf, rather than adobe reader..
i hate computers!
but cant help myself....