Just as a quick note, I have just setup my computer to run a dual Vista boot, one for general use with all the virus protections and Vista niceties, the other for CAD/CAM programs and AH. The one for clean one has only essentials, no virus or other protections, with IE set for maximum security.
Seems to work well, but unless you are comfortable with the tech stuff and disciplined in running scans manually, I wouldn't suggest it.
Dasher