There are no devices that record directly to MPEG4/Divx that I'd recommend for use with GB-PVR.
GB-PVR used to be compatible with the GO7007SB based hardware MPEG4 encoder devices like the Plextor TV-402u, LifeView TV Walker etc, but these were kind of flaky devices (or drivers?) and used by very few people so thay havnt been tested with GB-PVR for a very long time and not all their features work anymore.
These are the only hardware MPEG4 encoder devices that I'm aware of. Other devices that claim they recording divx/mpeg4 are just software encoder devices.
oh heck, sub, don't say that, I still use my trusty ol' 402U.
I'm still on a M10000 Mobo, because I'm both too tight and too poor to upgrade to a better CPU. Also, if I did, my girlfriend would make me 'donate' it to make room for other nice things like flowerpots, so its staying exactly where it is, recording shows in stunning picture quality and low disk space, but utterly rubbish lip-sync.
I use whats now a pretty old version of GB-PVR, and a EPIA M10K in a C137 box with the 402U connected by USB, and a Sigma (dont groan, sub) card for playback. The picture quality is frankly stunning with this combo, and there is no stuttering, but for some reason, as I mentioned the lip-sync is really bad. Still, it lends an air of low-budget kung-fu movies to everything, and if you watch Top Gear with it, its quite entertaining, because you know exactly what Clarkson is going to say 2 seconds before he says it. I use a 80Gb laptop drive, and I get enough shows with MPEG4 compression to not bother to upgrade. Its pretty green too, sleeps between shows, wakes up to get EPG, goes back to sleep again, except for the 402U, which is external and hence another PSU. Shame, if they made it in PCI format, I'd buy it in a flash...
Slay
-Slay
Config: VIA M10K Nehemiah, 512Mb, 80Gb 2.5" disk, PVR-350 (used for remote control only!), Plextor PX-M402U in Divx capture mode, Travla C137 case 120W PSU, Red-eye remote, C&W cable (old Telewest).
The GO7007SB devices showed potential but never really got popular, and never quite felt as stable as the Hauppauge devices, but otherwise they were alright.