To return the computer to the state you bought it (sans bloatware) you need a Windows disc. If you don't have one, you may be able to get Microsoft Support to send you one. Then just do a clean install.
http://www.mydigitallife.info/official-windows-7-sp1-iso-from-digital-river/
Thanks to Zelig for giving me this link not long ago. You'll still of course need your own legitimate product code, and you'll need to be sure to download the correct image.