I'm sure I forget a few differences, but:
Deluxe: 8 bit, full height but relatively short, external audio patch cable to sound card audio-in jack
Expert: 10 bit, half height but longer, internal audio cable
DV2000: 10 bit, full height but longer (than Deluxe), adds firewire
I find it hard to swallow paying so much more for a DV2000 when a separate firewire card costs less than the difference between the DV2000 and Expert. For the price of the DV2000 you might find another make of card offering hardware MPEG compression, though that's not what everyone wants, I usually capture to Divx instead... used to use MJPEG on a different card and every now and then I STILL keep checking the HDD, expecting it to be nearly full after recording something, only to be reminded that over 90% of it is empty still... bigger HDD but it's mostly thanks to Divx.