I am trying to run a licensed version of AutoCad 2007 from a Windows XP formatted hard drive. I have it in a hard drive enclosure and connected it to my Windows Vista Basic Laptop. I cannot get it to run and the compatibility wizard hasnt worked. HELP!

with a ,lot of high quality programs (autocad being one) when they are installed they make entries into the registry of the computer that the program is installed onto.
If you instal to a hard disk external then those registry entries MUST correspond to that hard disk drive letter (eg drive f:) If there are different usb or other drives in and out of the machine you will have problems with such programs on external hard disk.
One solution might be to install into a virtual machine, another would be to edit the registry each time!
Or finally you might have to buy a network version of the program!