first things first, if you have partition magic feel free to use it, HOWEVER, if you don't, just use and old linux livecd or installer cd, most come with FDISK, qparted or something like it.
Now, shared at this time has to be FAT32. Simply put, Windows can only read and write Fat32 and NTFS. Linux can read both formats too, however, it can only write FAT32 and not NTFS at this time. So yes, the most logical choice for shared space is FAT32.
Now if you wanna configure stuff, oh that depends. Would the common partition be used only as a "My Documents" folder or will it be used more as a place to install programs as well as store all your files.
Lets assume the common space is to be used as My Documents to store files/music/movies only, you don't game, and would like to get stuff done in linux. In this case i would suggest a small windows (20gb or less, 15gb might do). The logic behind this is that you don't game, so you won't have huge programs hogging the drive , thus little room is jsut fine to install the essentials. Make linux i'd say 40gb. Its just easier to keep all linux programs on one partition, and some can get pretty large (with all the deps and all). so just keep your linux large. Finally that leaves 40gb for storage. I think 40gb is enough to store your MP3 and AVI collections, and anything else you throw into it.
Now think logically, if you do play games, its wiser to keep them on the windows partition and so you might want to make it bigger (say 30gb) and adjust the linux and shared partitions accordingly.
