Ok... fresh install... setup a new user, to rule out any profile issues as well. No updates have been applied yet, setup SSH access and that's it. Progress as of now:
Removed kernel parameter "xforcevesa" from grub boot line - had to install in safe graphics mode.
Replaced "vesa" with "radeon" in xorg.conf
reboot... and a really expensive paper-weight is what I have... =) I think it's important to note, that I setup a new user after this install. GDM is not set to auto-login, and the lock up happens before I even see a login screen. X flashes like it's about to start, and the machine locks up.
for your perusal... no obvious errors, it should be working...
Had to add the Option "DRI" "false" to xorg.conf to get a desktop... Maybe it's just me, but the DRI option seems to be a bit more functional that the NoAccel option. I notice the difference when scrolling through Synaptic mostly. NoAccel is horrendous...
Just a wild guess but noticed from dmesg you're loading agpart so is it an AGP display card? If so, could try the normal radeon.agpmode=X switch to see if it affects the situation. (X is a numeric value, iirc -1 implies it's out of operation altogether)
I tried blacklisting both agp modules, intel_agp and agpgart - along with the option "BusType" PCIE in xorg.conf - but no love. Radeon doesn't seem to load without agpgart, but I left intel_agp blacklisted... still no difference.
I think I'm going to put an email into the Xorg mailing list and see if anyone has seen this behavior before. Xorg is the main issue here, what's causing the problem with Xorg is still unknown... but at least they may point me in the right direction.