M-audio, digidesign interfaced sound cards?

my new room mate is a profesional musician, he was in a band called "big city dreams" from florida to be exact. they got songs picked up for various mtv reality shows, he is a member of ascap and made some decent money from his tv royalties as a co-writer. his band broke up before they were suposed to go on warped tour, hes a pr executive now but he wants to start recording music again solo, and write music for other people too. he just needs a pc (or mac, or mac clone) to run protools on or prologic (what do you think?) and a m-audio or digidesign card.
we already picked out the monitor speakers and keyboard (probably m-audio) but im having trouble deciding on a sound card. he wants a 192 hertz card so he can record standard cd .wav files. he wants the duet and i think its pretty sexy but i told him it aint worth it unless he gets a laptop, and he doesnt want to. he also found nice 192htz m-audio cards for around 150.

hes not as well versed in digital recording as he is at actualy writing and playing music so im helping him build this computer.

i was a digital video engineer for a little bit, so i know my way around a digital studio, but i am not well versed in protools or logic pro or macs or sound card recording. any advise would be nice.

when he first came to me with his list he wanted a $1200 mac and the $500 duet and 300 dollar monitor speakers all bought RETAIL from places like guitar center, i was like "no way man, dont waste money like that" and got him to warm up to the idea of running protools on a pc and buying all the gear at places like overstock dot com. its 60% cheaper, thats what really made him like the pc idea after tallying the bottom line.

i just want to double check with the afterdawn comunity before he plops down 2 thousand on gear.

a few questions:

1. whats the difference between the m-audio version of protools and protools le? whats with the need for a digidesign or m-audio card? if i install it without the card will i be able to edit previously recorded clips just to test it out before buying the card?

2. how does playback work? will a crappy built-in sound card work for proper playback on the monitor speakers? or should he invest in a nice internal card as well for playback? are there outputs on the proprietary sound cards just for this reason? basicly how do i get super quality playback?

3. what are the best encoding and decompressing codecs for sound recording and monitoring?

4. what comp should he get? pc, mac, or mac clone? if it was video id say pc, use avid, and forget about fcp but the sound comunity still seems to worship macs. is there any disadvantage to using a pc to run protools and record music is what im saying...

and any special requirements for the computer for high quality sound recording, ether mac or pc? certain motherboard or firewire standards, ect?

5. what m-audio or digidesign external sound capture card should he get?

6. he has an old pentium 4 vaio tower from like 5 years ago, would this work? would it work just for getting his feet wet before deciding on a high quality computer? he said it was a "media pc" when he bought it so i think it might work, its not in front of me though so i cant check its specs.

hes asleep right now but when he wakes up i might add more questions.