First: if, by tandem, you mean SLI or anything close, just forget. GPU has to support it, and lowest GF6xxx supporting it was 6600.
Second: if you mean using display output from both cards, it s perfectly doable, easily in Windows 7, and probably easily in Windows XP. This is the one and the only way it may work.
Third: don't swear. It's bad habit.
Fourth: a guy once brought to me Socket A mobo with Pentium 3 squeezed into it, and he was swearing that this was working an hour ago. Sorry, no way.