I'm getting an "Invalid Boot.ini file booting from C:\Windows\"
"NTDetect failed" message when starting up. The computer does NOT boot up, it remians in this loops and the same message continues. I do not have my XP cd. What can I do?

Try running the XP repair. The administrator password is blank by default, so unless you actually set one, just press Enter.
If that works, type in:
COPY X:\i386\NTLDR C\:
where X is the drive letter for your CD drive.
Remove the CD and type exit.
Reboot your machine and see if that has fixed the problem

Simply type "FIXBOOT". Using the "FIXBOOT" command without any parameters will write a new partition boot sector to the system partition you are logged on to

Now reboot the computer. You should be able to log into Windows.

Umm.. lessee... fixboot to the best of my knowledge only repairs the actual boot sector code ie the code that gets loaded into memory. I think what you need is bootcfg in Recovery Console. That can be used to detect and build a boot.ini file. A command sequence might be:
bootcfg /list -shows the current file.
bootcfg /scan -finds all Windows OS.
bootcfg /rebuild -you select and build a file.
You will need some sort of XP cd though, so just borrow one. Almost any XP cd will do.