A couple of points.
* With dual-core CPUs still not being properly utilised by games (with a few exceptions, such as supreme commander) there is no noticeable drop in framerate when allocating CPU time to onboard sound.
* Onboard sound has progressed in leaps and bounds since 2002 and its associated audio codec terrors. The onboard sound you'll get with most new motherboards is great.
* Unless you have a good speaker system you won't be able to tell the difference. I've got a pair of creative stereo speakers and while good enough for what I do, unless I decide to go with 7.1 surround I'll not be complaining about my onboard.
* External sound cards are flipping expensive! Especially the BS that xtreme gamerz are sold; as Captante said if you're going for one, get the cheapest X-Fi and solve the exaggerated "omg framezloss" problem without breaking the bank for the top of the line model.
* If you do, however, have a good speaker system and want EAX for your games, refer to Captante's post above :thumbsup:.
Edit: F.E.A.R. is not multithreaded and assuming that you've got the Asus PW5 DH because you've got a Core 2 Duo, you've got a spare core for all that audio processing. And the onboard sound on your motherboard is pretty damn good. So I'd say that unless you've got a huge speaker system and really, really want EAX then no, $130 is not worth it because you won't notice the difference. Always judge upgrades, improvements and changes to your system and gaming etc by whether or not, for the price, you will actually see an improvement. The difference between 103FPS and 97FPS on a monitor with 85Hz refresh rate, for example, is nothing to you.