I have upgrade my MacBook Pro Duo core 1.83G from 80GB to 320GB as well...but I have also mess up the keyboard, then I bring it back to Apple store for repair. It cost me US$167(US$85 labor fee, the rest is the cost of the keyboard).
Oh well...now my keyboard backlight is more bright...and more clean
baka newegg.com just drop US$20 for the WD 320GB 5400rpm HDD today...