[wheezer11]

I have a new dell with vista home. I took my old hard drive out and put it in the new one. It had xp on it. It find the drive but not the operating system. What can I do to get it to see xp on the other drive?

[Elvandil]

Use VistabootPro
or
EasyBCD to add XP to the boot menu.

[DoubleHelix]

You took the hard drive from Computer 1 with Windows XP installed, and now connected it to Computer 2, and you want to boot up on it? Not gonna happen.

I've seen a set of instructions that you can do (after re-connecting the Windows XP drive back to the machine it came from), but results have been mixed, and it's a pretty involved procedure.

[Elvandil]

I answered your question, but DoubleHelix is right and you will only be able to boot, if at all, if the machines are virtually identical. Otherwise, you will need to install XP on the machine it is going to be used on for the right drivers to be present.