Hi Melanie,
I apologize in advance if this comes of as course, but your assessment of DMC's issue is just plain incorrect.
I just experienced the exact same issue as DMC just now after attempting to install immune attack. To address your point, the archive I used was the complete 519 MB (544,374,784 bytes to be exact).
As a matter of accuracy, virusese cannot simply piggyback on a file I've downloaded. I downloaded only “ImmuneAttackSetup.exe” from your server, nothing else. The virus in question was located within game-r.exe, the very executable that DMC could not find previously, since anti-vir never allowed it to be copied.
Game-r.exe is the executable that is run when you double-click 'Run Immune Attack' on the desktop, therefore virus is most certainly contained within your installer.
My installation was completely successfull except for game-r.exe not being present as my antiviru software prohibited copying. I'm still very interested in testing this game; if you could forward this issue on to someone invovled with the game's distribution I would greatly appreciate it, and I'm sure DMC would as well.
Feel free to email me with any follow up: wolach at gmail.com
-Adam