No sound from rear speakers

Hi,

I have just bought a Packard Bell (2414 I think) as my old pc was dying. I
have connected my old Creative 7.1 speakers (via the subwoofer etc) as per my
old pc.

However I only get sound through the front two speakers, I have tried to set
up for both 7.1 and 5.1 sound in all the options I can find and the strange
thing is if I run the speaker tests I can get sound from all speakers (in a
5.1 setup) including the sub, but only sound from the front two speakers for
windows sounds, music etc.

completely new to vista but is this a problem other people have seen?

thanks!