If the mobo has onboard audio you might need to download the drivers from Dell in order to get it working, particularly if you had a PCI sound card already in there. As a side note, it's really weird for a sound card to just up and die one day. Not impossible, but very unusual.
Personally I wouldn't screw with onboard sound, but I'm picky about things like that.
Like Malcom said, if you get another PCI sound card, go Newegg.com. I order hardware on a regular basis and I order from Newegg every time, no exceptions. Their prices, selection and shipping cost/speed is the best in the business, and their return/RMA process is fantastic as well.
If you're shopping for cards, Sound Blaster is pretty much THE name in the PC audio business unless you're doing production level mixing or something, and even then there are some nice high-end sound cards.
If you just need a quick fix and aren't real picky, a basic
Audigy SE would work well.
If you're into sound and have some nice speakers to pair it with, I can personally vouch for the
X-Fi Platinum.
There really aren't any compatibility issues to be concerned about. With a few very rare, bizarre exceptions, any Sound Blaster card from the past 2 or 3 years should work fine in any mobo from the past 2 or 3 years.