If you can't get up into safe mode you may end up performing a repair install or the manual method of engaging the system restore feature to roll back something you may have put on lately. Assigning passwords on a dual boot has it's definite drawbacks as you now realize.
For seeing the restore feature started you would enter the F8 startup menu for XP and select the safe mode /command prompt only option seen there. You enter the following command at the dos type command prompt. %systemroot%\system32\restore\rstrui.exe
The MS page on this is seen at How to start the System Restore tool at a command prompt in Windows XP
in case you end up mistyping the command in to see this done. That's easy enough to end up doing!
"gee how did that go now?