Yeah, the pc I've got has a SB Live Value in it. the sound card isn't wonderful but it's not too bad either. At least it has a S/PDIF output.
It's connected thru the S/PDIF to a Boston Acoustics sub, 5.1 channel sound with Boston Acoustics front speakers.
I don't have matching rear speakers, so I used these crappy ACS90 Altec Lansing speakers. (As far as I'm concerned, all Altec's are pieces of s***... they sound exactly like what they are.. a low quality, low impedance, small speaker inside a plastic box). Some day I'll go to the store and get new ones to replace them.
So I have a full 5.1 setup (howver the rears are on a table next to me, I don't have a long enough cord to put them in the back of the room. I lost that audio cable when I moved, I think).
And yes, speakers / sound card isn't the only issue but they are very much a main issue. A room with good acoustics is not going to make bad speakers sound better.
In the case of typical desk speakers the acoustics of the room are not very important, as you're going to be sitting in front of the speakers.