Just as a followup - i'm the one who started this thread :)
i got it working almost straight away. dom0 is set up thus:
pvscan -- reading all physical volumes (this may take a while...)
pvscan -- ACTIVE PV "/dev/sda6" of VG "vg00" [35.25 GB / 29.25 GB free]
pvscan -- total: 1 [35.28 GB] / in use: 1 [35.28 GB] / in no VG: 0 
vgscan -- reading all physical volumes (this may take a while...)
vgscan -- found active volume group "vg00"
lvscan -- ACTIVE "/dev/vg00/mail2" [2 GB]
lvscan -- ACTIVE "/dev/vg00/sbssgw1" [2 GB]
lvscan -- ACTIVE "/dev/vg00/gaia" [2 GB]
lvscan -- 3 logical volumes with 6 GB total in 1 volume group
lvscan -- 3 active logical volumes
my config file looks like this:
disk = [ 'phy:vg00/mail2,sda1,w' ]
root = "/dev/sda1 ro"
both dom0 and domU are all running debian 'sarge'. No devfs (I could never get devfs working and the general consensus was that it's a horrible thing that deserves to die and will be replaced by something better in 2.6. I like devfs but not enough to fight for it). No kernel patches. debian lvm10 package installed in dom0.