Hi! I wanted to Install Windows on a computer where debian was already installed. after istalling (no error messages), I didn't see any boot manager, just "NTLDR is missing"* I installed windows again. I saw my partitions, but then the same error happened again. I tried to install debian. I didn't see my partitions(!)
This question asks nothing specific about grml (or even Debian) so try asking
http://www.linuxquestions.org http://www.linux-tips.net
or similar. Grml is for sysadmins. But here is my advice.
Windows has a well known bug/problem/feature -- it does not like to be installed in second place. You have a bootloader problem and maybe a corrupted partition table. You can backup a partition table with
dd if=/dev/mydisk of=./mybackuptable.dd bs=512 count=1
and restore it with
dd if=./mybackuptable.dd of=/dev/mydisk bs=512 count=1
where the file mybackuptable.dd goes someplace permanent. But know what you're doing.
See dual-boot comments at http://os.newsforge.com/os/06/02/22/2221258.shtml for another clean dual-boot method. The USB solution leaves Windows hard drives totally unmodified and still gives a nice boot menu.
Or, you can install Windows to a QEMU image instead. Then it does not compete with Linux over the bootloader. This solution is also very clean.
On a partitioned IDE drive you need to install Windows first. Backup the Windows bootloader for safety. (Use a Linux live CD with dd command.) Fallback to default Windows if something goes wrong.
Then install Linux to another partition and boot. Add a stanza to lilo.conf to add the Windows boot partition to your boot menu. Execute lilo -v to make the new stanza take effect.
M