A company PC will most likely be run without welcome screen (windows2000 login look), meaning you should be able to select an admin account to log into (what you're looking for is called "local admin" and it is stored on disk, unlike domain admin password. If not(you see welcome screen), then do as above by fusion_gtx.
If you can see administrator in login, try to use empty password and "password", "Admin, admin, and Root, root. If they don't work, download ERD2007, or one of the pass cracks for XP. They will come as bootable cd image. Burn it to CD (not like data, but like iso). Boot with it and follow instructions (for ERD go to locksmith). You want to remove password, meaning make it empty. Then reboot, login as admin and set your own pass.