That sounds very good, althought the 18GB for FAT32 to transfer files between systems seems too much. To me I don't think there would be any file that's ~18GB and is use-able on linux system.

if you don't to transfer files why not mount your windows drive and then get the files from there? but maybe you have your reasons.

But anyhow, if I was you
I'd do

Seagate (80GB)
20GB for Win2k,
20GB for /
The rest of it for /home or anything similar

Seagate (80GB)
/home

and format all of the linux partition as reiserfs