Well, you only need 3 files to actually boot the computer:
ntldr
NTDETECT
boot.ini
Copying those to a CD and making it bootable would allow your computer to boot. Though, I don't know that that would get you past the winlogon problem, I don't think that it will, as this option would have you booting into the Windows GUI.
I think at this point your best luck would be with running the recovery console, if you're able to find your XP CD. I even dug up some pretty straightforward directions:
[pre]
1. Insert the Windows XP CD-ROM into the CD-ROM drive.
2. Shutdown and restart your computer.
3. Boot the CD-ROM, pressing R on the Welcome screen, or start the Recovery Console from the menu.
4. Select the Windows XP instance that you wish to access and enter the Administrator's password.
5. Type: expand <CD-ROM Drive Letter>\I386\comctl32.dl_ <Windows Drive Letter>\<Windows Folder>\System32
6. Type Exit.
7. Restart Windows XP.
If you cannot expand the files, repair the installation:
1. Boot the CD-ROM.
2. Press Enter on the Welcome screen.
3. Press F8 to accept the End-User License Agreement.
4. Press R to repair the installation, following the on-screen instructions.[pre]