Money,
If you want Darla, you really have to have a Intel Pentium...you'll have a hell of a time getting it to work with an AMD, if it's works at all. As for cubase having a AMD shouldn't be a problem, but I'd ask Steinberg before you buy it to be sure.
I also have an AMD processor (brand new) and I couldn't be happier with it, it out performs my old PII ten fold. I use SB Live Platnium and PG music's Powertracks Pro Audio 6.0 and the system works beautifully. A very quiet card, as quiet as my old Gina which I sold. Both products are highly recommended!
You'll have to do some hunting around for cards that work with AMD, but I'd avoid the ECHO line. Depends on how many inputs you need, and what equiptment you plan to use with it.
Good Luck,
Joe