maize said:

Just for completeness I thought I'd share my solution -

1. Pointed my browser to http://xxx.xxx.x.xxx/mfs/Recording/NowShowingByTitle
2. Selected the title I wanted to extract
3. Selected each number following "Part." This pointed my to the correct screen where the file FSID was located. It looked something like this:
RecordingPart 636978/13 {
CommercialSkipOffset = 0
File = 640880
Begin = 0
End = 814401
}
4. The FSID after *File* is the important one. Each number after part will link to *RecordingPart* where the individual FSID for each file exists. These are then used in bash-2.02# ./sendstream -s FSID1 FSID2 ... | ./nc -n -w 5 XXX.XXX.XXX.XXX 1200

Also another hint. You must buy the $19.99 component to Quicktime that allows viewing of MPEG-2 files. This isn't clear at http://www.fajkowski.com/tivo/. Unfortunately this is much slower for me than just using a tuner to stream my files to iMovie. It took over 4 hours to extract a half hour program. I was satisfied with the quality though. If anyone tell me how to write to ptvupgrade files, that would still be useful!

For answers to commonly asked questions, please refer to the
InstantCake Instructions and Release Notes,
Official InstantCake Discussion Thread, and the
Official PTVnet Discussion Thread