Something of a recap from irc, but for others who might be interested:

On OS X, this all just worked for me pretty much as described in the
manual. With a running venti and $venti set, I ran this:
	sudo vbackup /dev/rdisk0s2
and a few hours later got output like this:
	mount /vav/2008/0624 hfs:35eb...5a1b 2008/0624/1447
	# 2008/0624 14:47:07.178 /dev/rdisk0s2 hfs:35eb...5a1b
Adding those lines verbatim to a file 'config', I then ran:
	vnfs -c 16k config
and got back:
	handle da...0d
I don't yet fully understand the implications of that 16 char hex string,
so I'm not posting it here, but I didn't seem to need it anywhere else.
I'd previously created /mnt/dump, and then
	sudo vmount udp!localhost!2049 /mnt/dump
made paths like /mnt/dump/vav/2008/0624/Users/anthony exist.

On my venti server, I got a *lot* of these messages:
	venti/venti: bucket overflow XXX
but I think I understand that (this is a junk venti server used for
experimentation, so i didn't spend any time sizing things appropriately)
and it's unrelated to vbackup or vnfs. The only real problem from just
following the manual exactly was the instructions to mount something
like udp!localhost!nfs; my system couldn't resolve "nfs", so I pulled the
port number out of my local /etc/services and all was well.

Notes:
1)	This is really nice. Once I sort out issue #2 below and get a cron
script together, I've got my new cross-platform network backup system.

2)	vbackup from another host didn't work. Both are reasonably recent
p9p installs (the "other" system is from yesterday, and my venti server
is from a month or two ago), but i get:
	vbackup: vtconnect: vtversion: bad format in version string
I'll look into it more in any time I get while traveling.

3)	Speed isn't stellar, but is okay. Every compressed audio or video
file I tried worked without issue, but raw 640x480 DV was a bit much
for it. Mind you, that's with everything on one system and the venti
arenas on a HFS+ file system on an external FireWire 400 disk.

4)	It looks like libdiskfs allows vnfs to serve up arbitrary disk image
formats (hfs, ffs, ufs, &c), which is awesome, but it'd be nice if it could
also serve vac snapshots. Anything peculiar about vac that inhibits this,
or is it just a matter of extra code in libdiskfs (or in vnfs, to switch
between libdiskfs and something for vac)?

5)	I didn't do anything particular regarding a portmapper and have
never run nfs on this Mac, but ps does show I've got /usr/sbin/portmap
running. Maybe another small datapoint for John's problem.

Anthony