Running windows on a mac from a windows hard drive

So, I want to run windows on my mac, but I don't have a spare copy of windows. However, I do have a copy of windows on a Dell I don't use anymore.

Unfortunately, Dell never gave me a windows XP disc. Instead, they gave me a "Recovery disk," which I believe reinstalls the windows partition on the HDD. Is there any way for me to take this hard drive out of the Dell, hook it up to my mac using a Sata-to-usb cable, and run the windows from this hard drive on my mac?

I guess you could say it would be the equivilent of running windows installed to an external hard drive. Could a mac recognize windows already installed, or does boot camp have to do a completely new install for it to work?

Also worth considering: Maybe one could install the mac drivers to the pre-existing Dell's windows install before plugging it into the mac, so the mac's hardware can be recognized?

All and any thoughts/solutions are welcome.