Did you look at the mtrbd. audio chipset to see what maybe the "drivers" required or the audio card? It more than an educated guess to get the right drivers. Plus, many an OEM vendor once you enter the serial# or model series provides the specs for what's present or when shipped. But, I know the feeling. I honestly think it would have been better to start from scratch rather than repair the system "as is", but you weren't given the recovery CDs, ahhh the pain. 
enjoy -----Willy 
Have a problem with a Dell Dimension 4400 system with XP pre-installed.
Customer brought it in.....I don't see any shortcuts on the desktop nor a separate partition nor windows/cabs folder that would let you restore drivers or files that might be corrupt or missing.
She was loaded with trojans (AVG wiped them out after I got rid of the system restores) and nearly 1000 episodes of spyware....all cleaned up.
However, somewhere in the process of getting rid of the junk, one of those programs took out the sound (which was working fine prior to the cleanup).
Device Mgr shows SB Live WDM and Gameport....but nothing else for a SB Live card. Belarc reports the same two things and nothing else. I went to the Dell site for that system and there are only two SB Live files listed.....one is 512V and one is Digital.
I downloaded both, tried to install the 512V first and it seemed to go in just fine, but after rebooting, no sound, no devices listed in DMgr and nothing listed in Add\Remove Programs to uninstall.
I installed the digital file, got nearly finished with it and got a window saying there is NO SB Live detected in the machine so setup cancelled itself. It's a self-executable file that can't be extracted manually.....but I managed to find the files in the TEMP folder. Pointed the installation to that folder for the INF files and cab files listed in there, but it gets to one file (enu10k1f.sys) and wants the installation disk for Creative....and quits when I have to cancel since I don't get the option to skip it. I can't locate that file in the cab files in the TEMP folder either.
Went into the Bios to see if there was on-board sound that was screwing with a possible separate card somewhere and there is NOWHERE in the Peripheral Devices that lists a sound card....so it must be a separate card completely????? I'll open the case tomorrow to determine this for sure, but it looks like there is only one device to plug speakers into so it's not conflicting cards at least.
She's bringing me any and all disks that came with this system tomorrow afternoon so hopefully there will be something on one of them that will give the correct drivers at least. This was built in 2002 so hopefully back then, Dell was still handing out the installation disks for their systems......
GGGGGRRRRRRRRRRRRRRRRRRRRR
This girl had the nerve to tell me that she hates Dell and is going to HP systems for her next one...I nearly choked her. She wanted to know what's the best system......and I told her she was looking at a custom build by me for her next one.
TONI
Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic