I guess most of us make this mistake once....
The way I solved it was to boot XP, that still was bootable. After that I inserted my W2K3 CD and (re-)installed the Recovery/Repair console Console via
WINNT32.EXE /CmdCons. This reinstalled my W2K3 boot files and I was able to boot into W2K3 again.
Of course a partial installation of W2K3 would also do the trick, but this is way faster, and you don't need to cleanup afterwards. I use the partial reinstall when I haven't got a Windows I can boot to to use the winnt32 executable.
Hope this helps someone
