Trend Micro, McAfee, and FProt all have command-line scanners that are on multiple boot CD's (illegally) free for downloading and burning. All that's necessary is checking to see if they have current definitions loaded.* If you run them in a physical environment prior to booting into Windows, you can run all 3 simultaneously with no issues.

* if definitions are not up to date, I believe you can download the references from the respective sites for free and swap out the files on the image using UltraISO or the like.