Is there any way I can delete all my files, personal settings everything on my windows machine without reinstalling windows. The reason is I am leaving the company
It would be good to know how much is 'everything' in this case.
Here, 3 could become an interesting requirement on a Windows machine...
Further, if your company uses roaming profiles, most of your personal data is backed up on the server and there are secondary backups for recovery.
If roaming profiles are not in use, you might still have a domain login.
But, if neither of these are the case, and you just have a local-user-login on the system, you could delete the user and create a new one (that would still require administrator rights on the Vista machine -- which is a very likely case if your machine is not connected to a domain).
Before your profile is purged, you would of course delete all personal folders (that you created) along with their contents.
Again, if your company backs-up your system -- all this is already archived, so its not much use deleting these copies.
Hence, the real question is, whose access to that data are you trying to stop?
Update on your accepting my answer.
Use CCleaner while deleting the files in your personal directories. This program will allow you to write 0's over the existing data, which should foil all but the most determined users.
If possible then, delete your user profile by logging in with an admin account.
Also, if you're leaving on good terms, you could ask the local IT to delete your account while you watch. They'd probably be able to do that rather quickly.