Under the circumstances you describe, it shouldn't need a password, and hitting 'enter' without filling the password field should do it. There's no easy solution...
There are a couple of options. You could try and remove the password (whatever it is) using this:
http://home.eunet.no/pnordahl/ntpasswd/
The download is at the bottom of the page, with instructions. It's a bit complicated making the disc, but using it, once you have it, is simplicity itself.
Or this, as mentioned by Igorian:
http://www.ultimatebootcd.com/
Which also needs burning to disc as an image file using nero or something similar.
Or you could just start again. Assuming you have nothing on the machine you want to keep, boot from the XP disc to format the hard drive and start again. You don't actually need Windows 98 installed on the computer to use an upgrade disc, but you do need to have a disc/working installation key for Windows 98 - it will ask you for it during the install, and later on it will ask you for the XP key printed on the package as well...
Instructions here:
http://www.winsupersite.com/showcase/windowsxp_sg_clean.asp
This would be my favoured solution, because you are starting completely clean. Print them out, and off you go...
Failing this, you could try Linux. It's free! Maybe Ubuntu...