Just wanted to say that, if you’re on a tight budget, you can do a lot worse than M-Audio audiophile 2496 or better cards (about 6ms recording latency with ASIO / 24bit mix, and very cheap)
But, personally, I think a firewire external interface is probably the best bet, as it should be easier to protect from crosstalk / interference. That said, you’re likely to get the lowest latency with an internal interface.
I’ve heard good things about MOTU interfaces, which are well within the range of consumers, however I’ve not had the chance to use one myself so I can’t really compare it to anything.
** Some external interfaces (and some FW/USB cables) do a less than stellar job when it comes to shielding, and may not do an amazing job at keeping noise to a minimum. Read reviews, and check before buying.
** Disclaimer: personal opinions only, do not accept as undisputed fact, mileage may vary