I think the first question you have to ask is: in which OS I'll be working mainly? Or for what purpose you need them. Thinking in a 50/50 approach I would recommend to use 20GB for Windows, 10 GB for Linux Mint / (root) partition, and 30GB to /home or shared partition. Now, if you're going to work mainly in Mint I'd recommend you to format the /home partition into ext3 (though I prefer ReiserFS, there's a Windows program (http://www.fs-driver.org/download.html
) which can mount natively and transparently ext3 partitions).
If you're going to work on Windows, I would format that 30GB partition into FAT32, and use the 10GB for the whole
Sorry I've forgotten the swap partition, depending on your RAM I would choose between 1 o 2 GB. The lesser, the bigger
. And I'd take it from the shared (or /home) partition, as it is the big fish here
Hope I've helped!