I have faced this problem many many times before but I am asking it only now. This time I had a 40 GB HDD with Windows XP installed. The PC was to be upgraded with a 320 GB HDD while retaining the old 40 GB HDD. I starting installing XP on the 320 GB, Everything went on smoothly. When the installation was over, and I checked Disk Management, it showed that the 40 GB HDD as a Boot partition and the 320 GB as the System partition (or vice versa). When you have two HDDs with Windows already installed on one of them, and if you want the HDDs to be able to boot independently (each should be able to boot without the other being present), you normally remove the HDD with the pre-exiting Windows installation, and make a fresh installation of Windows on the new HDD. It has been some time since I have installed Windows and I goofed up. Now I want to to make the 320 GB HDD both as a System and Boot partition, without having to reinstall windows from scratch on the 320 GB HDD. Is there a way to do this ?

i think editing the boot.ini file and removing reference to the other OS should do it .or booting to windows disk and at the "R " recovery console command prompt run "fix MBR" to fix master boot record ,those are the things i would try