If I were looking just to get sound in/out of a pci slot and was using a mixer, I'd seriously look at either of these:
M-Audio Audiophile 2496 $99
E-MU 0404 $99
Both of pretty good A/D converters and the price performance is spot on.
If I absolutely wanted world-clock, s/pdif, and MIDI, then I'd move up to:
M-Audio Delta 1010LT $199.99 -- I'd like this over some of hte other cards in the $150 range as it's newer and the future driver support will be better.
If I had a lightpipe device and I didn't have an ADAT hub, I'd be looking at:
E-MU 1616 PCI $349
All that said, even for an older computer, I'd seriously consider picking up a PCI firewire/usb card ($50) and getting:
PreSonus FIREBOX $299 -- in mho the best interface on the market today in terms of price/performance ratio. As it's external it can move to your next computer easily.
I would absolutely stay away from SoundBlaster ... they aren't in the home recording market for a reason, they're a gamer's sound card only.
"The music business is a cruel and shallow money trench, a long plastic hallway where thieves and pimps run free, and good men die like dogs. There's also a negative side." -- HST
I agree with KP on the M-audio 2496. for $100 it's a great card
#4491....
Listen to King. I've got the Emu and it's great as well. All devices mentioned in his post have been proven and are well worth the money. A friend of mine got the audiophile and that's a great card as well. Can't go wrong with either of them. 8)