I have the same motherboard but with an Athlon X2 (running Leo4All 4.1). I would recommend LawlessPPC as well since it installs the Chameleon bootloader by default which is needed for Phenoms. Leo4All 4.1 has a Chameleon option as well but may be harder to get working because of its' numerous install options. Also make sure you have SATA drives since the SB700 isn't supported or else you'll get the dreaded Waiting For Root Device if you try to boot from IDE.

As far as graphics cards go I can tell you that the HD 3850 works perfectly (using the drivers that R0GUE referenced to) but it has a fan. Don't see why the 3650 wouldn't work but I can't tell you for sure; I'd prob go for a GeForce since they tend to be the most compatible.

Good motherboard btw -- after some tweaking I was able to get about a 20 second boot time

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iPC 10.5.6 w/ Voodoo Kernel | AMD Athlon X2 5000+ BE @ 3.01 GHz | Gigabyte GA-MA78GM-S2H | 780G North & SB700 South | ATI Radeon HD 3850 | 2GB DDR2 800 | 2 x 500GB SATA HDD | 1 x DVD-R DL SATA