Hi rkremser,
Pain is pretty close from what I have seen. You can get by with about 3 gig for / need 256 ~ 512 for swap if mem is 256 or less. The big issue is the the myth partition because with a small drive, you don't run of space, you run out of inodes..
Assuming the ~ 8 gig suggested, what you could try is do the partition for the ~512 for swap and then give everything else to / Mind you this is not really good however it should work very well for most everything except tv / video recordings. Music, gallery images, email, etc. As a frontend it should also be ok as the files are not stored locally.
Once you have partioned hda1 as / hda2 as swap then try a manual upgrade as that should partition the / and build everything including /myth. You have to manually make the swap and probably have to fix the /etc/fstab to see it. I think that is in the pamphlet if not it is simple to do.
Try it and let us know if it flys. Wondering why it will work with out a myth partition? Because it makes a myth folder but it is using smaller drive blocks so you don't run out of inodes
Good luck, I have done A16 on a 6gig with ~30 minutes record time available.
Mike