Just like Monkey Wrench said, it's pretty easy stuff, assuming your old sound isn't integrated to the board. The new card will come with instructions on how to install it. However, the steps they won't tell you are;
First, make a restore point. Always do this before software or hardware changes. Saves your bacon every time.
1.) Uninstall drivers; If you haven't already, log into an Administrative account. Go into control panel, system, device manager, and under "sound, game and video controllers", click your card, and click "uninstall". That prevents a nasty conflict with your old and new cards' drivers.
2.) Next, shut down and power off.
3.) It's now time to open the case. Be fore-warned, some cases can be a pain in the hind quarters to open. Some hinge open like a book, some open backwards, some even come apart in sections. This is hands down the hardest part; but once you figure out how to open it, it's pretty easy. Chances are, if it's a Dell, they're using pretty much the same case my sister has; it has a couple of buttons on the top-back and bottom-back. You'll lay the tower on its' side, push the buttons while lifting up. The whole case should open like a book.
4.) Personally, I work on PC's with the power cord attached, and use the chassis to discharge static electricity. It's all personal preference. You could easily ground yourself by touching the screw that holds the face on an electrical outlet, or spend the cash and get a ground-wrist-strap (overkill, in my opinion).
5.) Next, now that you have your case open, locate the old card (shouldn't be that hard). At this point, there are two possiblilites; card and built-in.
If it's built in, you'll have to enter the bios and disable it. That is done simply by pressing the right key (it varies from bios to bios, but dells are usually delete; it'll say when you boot the pc). Once in the bios, page over to peripherals, find "Onboard Audio", and make sure it's disabled. The bios will actually tell you how to toggle it off and on.
However, if it's just a card (most likely; dell didn't use integrated stuff at that time), disconnect your speaker wires, if you have not already done so, and the cdrom analog audio cord. Remove the screw (might be a phillips, a torx, or just a hex-head, different pc manufactuers use different types), and pull GENTLY but FIRMLY up. The card will literally slide free.
6.) Make sure the socket is free of dust (you're prolly thinking 'holy moley, that thing is dusty inside!!'... PCs are natural dust magnates), and gently line up the new card, and press firmly yet gently to seat it. Replace the screw, connect the analog cable, and reconnect your speaker lines.
7.) Next, close the case up. Stand the PC upright, and the hard part is over. Turn on the PC, and let windows boot up. Log into your Administrative account, and let the plug-n-play part of windows do it's thing. Have your drivers disc handy; it may end up asking for it.
