Let's correct some of this misinformation. Firstly, the board is not bad because it only supports DDR2 memory. It is an AMD board and all AMD processors use only DDR2 memory. DDR3 is coming but not here yet in AMD land. Boards for Socket 775 Intel processors only support DDR2 memory as well because DDR3 memory is only for the Core i7 processors. Boards for the Core i7 processors all support DDR3.
The drivers for the on-board audio are not bad. They work just fine with Vista. Actually, this is a fairly deluxe mainboard. Nice quality, plenty of I/O. I've used it many times in builds. The people giving you "advice" have no personal experience with it.
The problem with judging sound quality is that it is impossible to make meaningful comparisons without a bias controlled test. A sound card is nothing but an ADC/DAC with preamplifier IC's connected to them. It converts between digital information and analog wave forms. All of them do the same thing and there is no meaningful audible difference between any of them - including the ADC's in high end recording studio units. I've been doing bias controlled test on DAC's for over ten years. One board may have a more powerful amplifier than another and that will normally make the output a little louder at any given volume setting. Louder is interpreted by our brains as better. That's why a bias controlled listening test would include, among other things, exact level matching.
Personally, I use an outboard recording interface connected by firewire that cost several hundred dollars. Does it sound better on playback than the Realtek on-board audio? Not even a little. I use it because it is far more flexible for recording and allows me to connect professional level recording equipment. A Soundblaster card is a toy compared to the recording interface.
I realize people rave about sound quality. Unfortunately, they don't understand that most of the differences they hear in this kind of situation aren't generated by the equpment but by their own biases. Hearing bias affects us all. Been there done that for a long, long time.
So the question is should you buy a sound card? Maybe so, maybe not. If "sound quality" is what you want, then I would say not. If interface with better software is important, or recording is your goal, then perhaps so.
If you want to improve the audio from your computer, the best thing you can do is to install better speakers, including a small subwoofer to handle the low frequencies. You can buy speaker sets like this anywhere computers are sold and they will help meaningfully - even in bias controlled listening tests.
I apologize for the rant.
