I'm working with a WD 1GB HD with my 91HD.
I had to create my own partitions in order to make it work, I don't know why - but it's a fact.
I'm using a first linux EXT2 partition for the receiver (300GB) and I created an NTFS partition for my own usage (the 91HD won't touch it) for the remaining 700GB.
Before I created the EXT2 partition manually, it wouldn't work.
the fuse.ko and the userspace application at
http://www.megaupload.com/?d=KBUJSZLQ
I formatted my new USB HDD (1TB) in ext2 (don't forget for very large HDD to activate the swap via "swapon /dev/sda1" in my case) so it will be rw compatible with all the images (E2 or DGS, etc), and on my Windows PC, I installed the drivers developed by "Ext2Fsd Project" (http://www.ext2fsd.com/) in order to be able to read and write when I want to connect this HDD directly in USB on my Windows PC.