Major Critical Dilemma:  Need Help ASAP

How is it POSSIBLE that unwanted files have been stored to my work laptop all HOURS of the day?....many in temporary internet folders but others in My Docs, My Music folder?  It SEEMS possible that my username and password were stolen and used by others to view these documents, but how did someone save these to a folder in My Documents, actually on my PC, without physically TOUCHING it?  That is, much of the file save or access times were in the middle of the night while sleeping, etc.
Nortel Contivity VPN is used for remote access to our intranet, along with home WIFI (Lynksis, unsecure) which could EXPLAIN some of this activity, but I'm really a novice here.
Please help, I've been hacked!



PS...should have noted that sometimes, after working at home, my PC will be kicked off VPN, but will remain on WIFI if that helps or adds a possible wrinkle.
Thanks to all.Contact your system administrator.My System Admin is the dept that told me of this activity and file saving, they are unable to offer a reasonable explanation however as to how this occured or could occur, other than to say me or someone else has used my computer.  Remote access for loading of software does happen and it is safe to assume my password is/was in the open...could this result in outside access to my laptop and actually saving files to a folder in my Documents?  So far, some say yes, others say unlikely, but I believe it can be done, but don't know the process or technical expression as to how this can actually be accomplished.  Please help or explain if you can...thanks.First of all, request a new password.

Disable Windows XP Printer and File sharing.
Disable Windows XP Remote desktop.
Post a HijackThis log.