I have the M52 8215-MUB and was successful in upgrading its video card using a PCI-e 1x card. It will now easily play the new Flash 10.1 videos as well as 1080p Blu-Ray rips at about 40% CPU usage (It's a Pentium 4 3GHZ processor with 1GB ram).
Actually, I took a PCI-e 16x card and snipped off the pins as described here:
So if you can't find a 1x card just get a 16x card and a razor blade and start cutting! These machines make really nice HTPCs because they're relatively small, easy to add Blu-Ray players too, gigabit ethernet, etc.