It doesn't happen every time I go on it, but this is actually the first time it's happened outside of the game; before, after a while of playing Far Cry 2, I sometimes get some strange texture effects - eg. the sky starts flickering or something.
But this time when it happened (I usually turn off FC2 and restart it to 'fix' the effects), I turned FC2 off, and it was affecting explorer now.
Could my graphics card[s] be on its way out? My computer's only 3 years old.