Windows XP Adding Vista To XP Boot

I Have done this before but I can't really remember how, I have XP installed on my master and Vista running of the slave, I had to boot configuation running fine but I had to reinstall XP due to issues which overwrote my boot config, I tried adding it to the boot.ini but It just sitts when accessing it, and i can't simply unplug one harddrive as my boot config was set to be on the primary harddrive, I know theres a way to add Vista again, if anyone knows how please tell me

no problem my friend click in my computer propereties click to advanced in startup and system recovery click on setting(the 3third) press edit... and add this :
multi(0)disk(0)rdisk(0)partition(2)\WINDOWS="WindowsVista" /fastdetect /noexecute=alwaysoff /usepmtimer

or use diskpart or if the pc boots with vista install easybcd and add xp...

I used Vista Boot Pro

VistaBootPRO - Dual Boot Windows 7 or Vista with Windows XP