Yes, there is such a disk. I've used one quite a few times in the past and blanking passwords works like a charm. Unfortunately I don't have the floppy anymore and I couldn't remeber where I downloaded it from if my life depended on it.
There is another way of getting administrator privileges which requires only the installation CD for XP Professional and a valid serial number. It might seem destructive at first but I've tried it and it works ok. Here's what you do :
1. Boot off the CD and do a Repair (not from the recovery console)
2. Setup will copy all the dll's... then your pc will restart and start the next step of the repair (were it give's you all bunch of info about XP)
3. On the left side of your screen you'll see the progress bar. As soon as you see "Installing Devices" press Shift+F10. This will open a command prompt.

Now you're in bussiness.
4. From the command prompt, type nusrmgr.cpl. This command will open the user profile screen were you can reset any password (including the administrators) or create new users.
5. After you're done messing around with the accounts, simply close the user profile window and the command prompt and let setup finish the install.
6. That's it, as soon as the install is done your password will be reseted and you'll have access to everything.
Hope this helps.
EDIT: I googled around a bit and
http://home.eunet.no/~pnordahl/ntpasswd/ seems to be ok. However, do keep in mind the fact that I've never tested it.