i use these tips every few months to speedup my pc .
my laptop is a 4 year old acer aspire that runs windows xp and a lot of free opensource software.
most of the clean up steps and apps will also work in windows vista and windows 7
Step 1: Speeding up windows part 1
goto start > all programs > accessories > system tools > disk cleanup
select the c:\ drive > select al catagory's and press ok.
this wil free up system space and will make you laptop run faster ,because windows will not have to keep track of all those unneeded files