It depends. The stock 160GB S3 HD drive comes with 2 MFS pairs, partitions 10 and 11, and partitions 12 and 13. Using the MFS Live cd or WinMFS to upgrade to a bigger drive results in a third MFS pair being added to fill up the extra space, and that brings you up to 15 partitions, which means you can add one more using the jmfs cd v1.04. The catch is that when the 3rd MFS pair is added, that has to use up all of the space on the upgrade drive. If not, then even a small amount of leftover space will, because of the way the Apple Partition Map scheme works, be labeled an Apple Free Partition (that's right, unpartitioned space is a partition--now you know what Apple meant by "think different"). When that happens the Apple Free partition becomes partition 16, and that's the limit per single TiVo drive. The first thing jmfs does is "Xerox" the source drive to the target drive. That means it copies the Apple Free partition as well. Then when jmfs goes to expand by adding a single MFS media partition, that partition is the 17th one on the drive. TiVo no like that. TiVo throw up. In my experience so far, the otherwise excellent MFS Live cd leaves a little space when it adds the 3rd MFS pair, and there doesn't seem to be a way to juggle anything to prevent that. WinMFS, on the other hand, will use all of the available space. So use WinMFS's mfsinfo to get the partition map and copy and paste it here so we know what we're dealing with. Alternately, use the MFS Live cd and pdisk -l /dev/sd"x" (where "x" is a or b or whatever is necessary to refer to the TiVo drive and not your Windows drive or DVD or whatever) and redirect the output to a text file that you can paste here. Refresh my memory, do you have a TCD652160?