ok the spec for my shiny black box of audio editing goodness is thus
AMD Athalon 64 3200+ (winchester chipset if that makes any difference to you, supposedlly better for overclocking)
1 Gig of Crucial Ballistix PC4000 DDR RAM, very nice RAM. a gig as all you're gonna need really, even if your doing some heavy editing it'll be fine
Motherboard is an MSI K8N Neo2 Platinum. not much to say, its a motherboard and it fits all the stuff lol. it has onboard soundcard, 2 network card connections, 4 USB ports a firewire port as well as an optical out on the soundcard. a few other nifty things but basically its just a nice mobo
hard drive is a 160 gig Serial ATA Seagate Barracuda 7200. ide recomend this brand as they well priced and extremelly quiet.
the case i got is the antec sonata. its designed to be a quiet case and is very well designed. its a bit pricey but i cant recomend it enough.
thats probablly all that would be important with regards to audio. youve seen the sound card that im ordering.
also you will never have problems with space on this MOBO, it has 4 SATA sockets, so if you really wanted to you could have 4 SATA hard drives which would give you 800 gig. i dare you to try and use that much space up lol.
as far as i know USB hard drives are perfectlly fine to use. with hard drives i wouldnt worry too much about it being slow since the majority of the information youd be playing with would be loaded into the RAM anyhow.
desktop vs laptop debate id go desktop but thats just personal; preference. my mates brother has his laptop as a recording studio and its good enough to run a prefessional studio off.
i bought all the stuff for my desktop off overclockers.co.uk and built it myself. one place worth checking out for prebuilt audio computers is redsub.com. i had a look there but decided i could do better myself lol.
all in all my desktop has cost me £700 for the basics. i then spent £200 on the GFX card and a nifty wireless keyboard and ive spent £330 on thesound card and a mic.
with regards to the firewire hub buisness as far as i can tell it wouldnt compromise the audio quality one bit. the signal is converted to digital in the M-Audio device so it traveling through the hub etc wont do anything to it
hope all thats helpful. if you really want i can give you a full rundown of my computer but i think thatd do more for polishing my ego than actually being useful to you lol