If you cant wipe it then you'll need to adopt a methodical approach regarding where you're personal data is stored.
Browsers: All browsers allow you to delete cookies, history logins etc - a quick google search will give you instructions on how to do it for each one thats installed.
Documents etc: This article is quite old but still valid
http://lifehacker.com/5625313/what-should-i-do-to-my-work-laptop-before-i-leave-my-jobOther programs: Uninstall anything you've installed, if they keep information then they'll usually give you an option to delete any folders files etc that hold user data.
If you're confident about doing it, a quick way is to reinstall Windows from the recovery option - it may be worth speaking to your IT dept about that.
JF