Also consider the Focusrite Saffire models: 10 I/O & 26 I/O. I have the 26 I/O and am very happy with it. I too considered the RME interface which as others have eluded to is quite a worthy contender but went with the 26 I/O being the less expensive of the two.
I second the Motu. I've been running an 828mkII on my XP laptop for over a year with ZERO problems.
Be SURE to have a motherboard or Firewire card with TexasInstruments or Lucent firewire chips (a REQUIREMENT by Motu and most other interface manufacturers for them to work!)