you can reset your password, no problem. Just search a bit on google for "windows xp password retrieval" or sth similar and you will find quite a lot of diffrent programs to solve your problem. Usually they're very small - fit on a floppy disk if you still use it... so there should be no problem downloading it.
Then you just insert floppy disc or CD-ROM into your computer and reboot so the program loads before your operating system (I'm talking for windows xp) and you should see a nice menu and step by step instructions which will guide you through the process.
If you're not incredibly stupid you can't possibly do anything harmful to your operating system... just follow the instructions. And my suggestion is that you choose to pick no password at all for administrator account than to set it to one you choose... don't know why but it usually works better. Anyway, if you get stuck just simply take the media out (floppy or CD) and reboot computer and call a friend who is a linux geek