Vista Dualboot using USB External as second O/S

My problem should be simple to resolve,maybe. I've a new HP a6040n desktop with Vista Home Premium O/S. SATA 320 HDD.(system still in box). I'm using a 320 GB Seagate IDE HDD (with XP Pro installed)for my classes. It is set in a 5 1/2 carriage so that I can take it home to do my studies. I also have an external USB 2.0 case which I can mount my HDD into.This HDD has to stay mobile . I have all cables and adapters to install either way. What is the "dualboot ini." command for Vista, and which is the best way to set this up. Both O/S are legal!
 
FYI: I decided to try another way. I guess there wasn't anybody that could offer any suggestions. I went with a "IDE to SATA Dongle" for my IDE HDD. Then I installed an dual boot manager to configure my HDD'S. You can find the tool at "www.vistabootpro.com" its a free downloadable tool which is user friendly and takes out all of the problems of having to manually edit Registry Files in "system32", a
s I'm sure that some of you people already know Vista registry is not the easiest thing to navigate in.
Hope this might help others out there.
 
Back