If you downloaded it from both the Xordan server and Bittorrent I think you can be sure that not the downloads themselves are infected but your computer. Verden is probably right that a worm infected the files during/after install.
I recommend using an online virusscanner like
http://housecall.trendmicro.com/uk/ so you can scan your pc without having to install another antivirus scanner. If that scanner finds no virusses at all and if Comodo is up-to-date an a full disk scan by it doesn't reveal anything, it's probably a false positive. If it's a false positive you can report it to Comodo or put the PlaneShift folder on an ignore list.