In reply to Caspar:
If you were to go during any other time during winter then you'd be a braver man than I am. The climbing season is roughly Nov/Dec/Jan/Feb and early March. Even during these months the weather can be extremely serious. Climbing it outside of these months would be extremely difficult, even on the non technical normal route.
I'd advise you to do a little research. Check this site out for good logistics/routes/general info.
www.summitpost.org/mountain/rock/.../aconcagua.html