Spending the extra on some good speakers will give you more of an improvement in sound quality than getting a better sound card.
The only real differences are stuff like EAX hardware (for adding environmental effects/echos etc, without any real performance hit), and the amount of CPU cycles that are 'stolen' by the on-board sound. I've never found EAX adds that much to a game (but with a really good surround setup it might.. *shrug*)..
As for using up CPU time, THG did an <A HREF="http://www6.tomshardware.com/game/20030405/index.html" target="_new">article</A> on this sort of thing a while ago. It's a bit old now, but shows the basic premise. Looking at some of the <A HREF="http://www6.tomshardware.com/game/20030405/sound_for_games-03.html#quake_3" target="_new">benchmarks</A> You can see the effect on games of good audio processing hardware.
<b>But</b>, (and this is a big but) the Doom III engine (which will be powering a lot of future games for the next few years) in its present form <b>DOES NOT</b> actually make use of any of this hardware - it's audio is done entirely on the CPU, so a better sound card will make no difference in this case. They may change this with a patch, but maybe not. Other game engines will likely benifit though.
So basically, quality-wise, it'll make little difference, and performance-wise, a good sound card <i>might</i> give a couple of % extra performance - but with a decent A64 system you're extremely unlikely to notice that anyway
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<pre>You can always tell how bored I am at work by the amount of effort I put into my postings.... Today I am bored...</pre><p>
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