Reporting a steam cheaters... am I sol?

[ameratsu]

I was just playing a public match of left4dead and one person was cheating. As a survivor, he'd track special infected (as in have them in his crosshairs and follow them) before they actually spawned. You are not supposed to be able to know where infected are before they spawn, this is rediculous! Watching him from the first person perspective made it clear he was playing with some kind of autoaim, as well as the ability to see pre-spawn infected.

I checked valve's website and there is no mechanism as far as I can tell to report cheaters, which kinda sucks. Is there any way to deal with cheaters other than valve's VAC, which apparantly cheaters have got around.

Thanks

edit: lol my title sucks