How install dual boot?

I have installed a second instance of XP on the E: partition of my machine. The command line interface of the Recovery Manager (booted from the reinstallation CD) confirms that XP exists in C: and another in E: However the Boot Manager (F12 at machine turn on) continues to give me the boot alternatives only of "normal", "diskette", "Drive C:", and "CD". The 2nd XP installation did not add drive E:'s copy to the boot manager. How can I accomplish that? Why do I want two XP's on one box? The registry in my c: drive XP installation is so broken (I know, I shouldn't have done that) it won't boot or let me in Safe Mode. I have been given a procedure for editing C:'s registry using data from drive C:'s restore points. It involves moving the hard drive to another machine for the editing. I'm reluctant to do that. I avoid putting another machine at risk by booting from E:, editing the registry in C:, restoring C: to full function at an earlier restore point, and then removing the extra XP installation in E: The machine is a Dell Dimension 8200 with two internal drives (2 partitions each) and an external hard drive. C:'s XP is Fix Pack 2 fully updated. E:'s XP is Fix Pack 2 not updated from Dell's reinstallation CD. All the drives are NTFS formatted. I have Partition Magic but it is by download into C: so I don't know how to get at it.