The steam forums have a VAC banned section, in every thread nearly, it says once you are vac2 banned you are NEVER unbanned. VAC1 bans could last from 1 year to 5.
Yeah, but unlike what someone said up there, VAC2 bans are FOREVER.
http://support.steampowered.com/cgi-bin/steampowered.cfg/php/enduser/std_adp.php?p_faqid=370
Go have a look at that.