Are you trying to do repair or restore? Repair is done in DOS, restore has a GUI. If you try to do a repair, you'll get a DOS prompt asking for a user name (admin) and password (blank if you didn't setting, which is what we're hoping, as you don't remember it). If you get to a DOS prompt from there, you entered the correct password. I think it says incorrect password if it's wrong. At the DOS prompt, you can type (I believe) /help to get a list of what functions are available.
If you're trying to do a restore, I didn't know that you needed one to do a restore. If you do and leaving it blank doesn't cut it, I don't know what to tell you beyond a reinstallation (lose all data).
When you boot from the XP CD and it finishes booting, it says "Press Enter to Install Windows XP" or "Press R to enter Recovery Console" (repair). To restore, you hit enter, it searches for existing installations, then it will locate your current installation. It will then ask if you want to restore that installation or do a clean installation. If you, instead, hit R, you enter Recovery Console (repair) and that's what's DOS. I don't think you can do anything in recovery console unless you know what specific file is causing your dillema so you can copy a new version off the CD.
If you already knew this and I'm wasting your time, I'm sorry, but I can't really tell what you're trying to do.
Z