I'm on an Athlon dual core 2.4Ghz, 2GB Ram, 500GB 7200rpm SATA drive
Audio Interface: Saffire Pro 40
Mics: SM58,SM57,SE2000,RODE NT1A,SE4a
Midi controllers: Remote 91SL, Akai MPD42, BCF2000
Synths/grooveboxes: Novation A Station, Yamaha AN200, Korg ESX
Pres: Art TubeMP V3
FX: DBX266XL Compressor, Lexicon MX200, Electrix FilterFactory
Other: Lin6 Toneport, 2x Behringer PX2000 patchbay
Instr: Bongos , Yamaha Pacifica guitar (badly out of tune, I just use it for some interesting fx), Yamaha DGX620 Electric Grand
.........................................yes it's an obsession.........
Monitors: Tannoy Reveal 5a + hifi speakers on a JVC !X333 amp
Rastardley: the 192's inputs wont take a hi-z guitar input - you'll need a DI box to get the signal right - look at the Lin6 toneport GX - basically a DI box with an amp plugin OR you could look at getting a preamp and a mic to record direct from an amp.
Additionally, you'll need an extra program to record your guitar into as Reason wont record audio - I've used Audacity when I needed to do this - freeware of course
Phooey: I'd lean the other way these days - the new Macbooks have apparently dropped the firewire ports completely, which rules out a fair few really good interfaces!!!
to be fair i've always been a PC man, but thought i'd mention it.
RB83: Firewire is better for multichannel - though USB2 can handle 2 in 2 out with respectable latency figures I wouldnt trust it on an 8 in 8 out interface.