How did you manage to get a 200gb format in Fat32? I bought an external 500 gig drive, then tried to format the first partition as Fat32 in the biggest size I could get it. I'm using WinXP Pro. It would not allow me to format the partition as Fat32 until I took the size of it all the way down to 32 gig. Go up to 33 gig and NTFS is the only choice.
Anyway, that might be part of your problem. With my first partition formatted as Fat32, 32 gig, the 360 reads it just fine. I thought maybe I could create multiple 32 gig partitions, but unfortunately the 360 only looks at the first one and ignores everything else.
The main problem I'm having (and the reason I went digging through these forums in the first place) is that I need to find a way to get files that are larger than 4 gig onto that partition. Fat32 doesn't support filesizes over that limit, so either some trickery will have to be done to get the files on there, or the 360 will have to somehow be able to recognize NTFS. I imagine you're going to run into that wall yourself once you get the 360 to recognize the partition. WMV files in HD tend to be over 4 gigs usually.
Kind of a bummer to buy one of these huge external drives and then find out the 360 doesn't play too nicely with 'em. Either a hacker will miraculasly figure out how to get it to work with NTFS, or MS will get around to adding NTFS support.