Assuming 10Gb for system data, 15Gb for your Music, 15Gb for your movies, and 5Gb for CS3, you're looking at having about 15Gb free, which would be a bit on the low side, in my opinion. I would suggest at least 120Gb.
With regards to RAM, the more the merrier. I recommend at least 2Gb for Macs these days. My MacBook Pro CD has 1Gb, and it is a little pokey for me. I'm planning on upgrading to a C2D with 2Gb soon.