There's a lot of answers in this thread, but I'm not sure all of them are suitable.
- Remove BIOS battery; has nothing to do with the OP's question.
- Sp!ke is correct in that you should not be able to remove user accounts unless you are logged in as a user that has Admin rights, or unless you are logged in as the actual Administrator.
- If you deleted the user accounts by deleting the relevant folders in Documents and Settings, then the users should still show up on the welcome screen - Windows will simply create a new profile on boot.
- Adding to Kully 124Coupe's instructions;
-- step 2a: Click the name of the user you want to log in as. Their name will then be highlighted. You can see if they are an Administrator by looking in the next column over - "Group". Now proceed to step 3.
- Kully is also correct that Hiren's Boot CD is definitely worth a look at. I've never used it to recover passwords, but if it's as good at that as it is at everything else it's supposed to do then it should work fine.
- The Linux Boot floppy I mentioned isn't all that complicated and it would be relatively easy to talk you through it. It's all command-line stuff (press 1 for this option, etc) and can look somewhat intimidating if you've never seen anything like it before. It should be possible to create a bootable flash (USB) drive with it on, however.
Not having an available CDROM or floppy adds an additional complication that you could do without. Would be good if you could find the power supply for that CD drive.
Finally, as Spinal said, a clean install could really help out if your current installation is hosed because of this. Clean installs can also make your computer feel a lot faster, especially if it's had over a year's use!