Here's a condensed answer: Firewire is a very fast interface although the newer USB 2.0 supposedly may give it a run for the money once USB 2.0 devices become more common. USB 1.0 devices are the slowest although I use a Tascam US-122 interface, which uses USB 1.0, with my laptop for 96k/24bit stereo field recording and haven't had the first problem with it. The problems seem to come up with interface speed when you are trying to run more than 2 I/O's of audio at one time. PCI is very fast and is my personal preference for a desktop audio interface. On my studio desktop, I use the M-Audio Delta 1010LT PCI interface for audio and MIDI which meets all the specs, has plenty of I/O's, and has given me no problems at all.

Here's a company that makes desktops especially for audio production:
http://www.digitalaudiowave.com/

I think the only reason you might want a specially-designed audio desktop would be if you plan on using it in the same room that you are using for recording. The so-called "audio desktops" have baffling to reduce the noise from the power supply and air circulation fans but are otherwise pretty much ordinary desktops.

[This message has been edited by The Pro (edited 11-05-2003).]