Normally, IDE0 connects to the hard drive/drives and IDE1 connects to the optical (CD/DVD) drives.
Did you add the new optical drive (hp cd-writer 9700) to the cable another optical CD/DVD drive was connected to or did you add it to the one the hard drive was connected to?
Since you were inside the computer, moving things around, the first thing to do is check to make sure all the cables and connectors are firmly seated, on the mother board and at the drives themselves.
If everything is okay, then see this Microsoft Article for how to rebuild your boot.ini file:
"Invalid Boot.ini" or "Windows could not start" error messages when you start your computer
If you don't have a Windows XP install CD download and create a bootable CD from the .iso file here:
XP Recovery Console
You don't burn the iso file itself to CD., you create a CD from the iso file using your CD burning software. There is a good freeware burner called
DeepBurnerwhich will do this. Another called
ISO Recorder is also very easy to use.
Boot the CD and at the first opportunity, enter
R to start the Recovery Console.
Next, choose which XP installation you want to login to. Normally this will be 1.
Lastly you will be asked for the Administrator password. Just press the Enter key as the Administrator does not have a password (unless you gave it one, then you would enter it).
Now follow the directions at the Microsoft site.