That is so scary, I run a Inter Core i7 with 4 Gb of RAM and a Radeon 4870HD but Game of Thrones in 720p still lags every now and then. I have no idea why either, it's almost like it's at the disks since there is no big cpu hog (100%). But I run only SATA-disks and have no other load on them while playing.
In windows 7 (32bit), I have no issues at all. I can even play it over my local network without an issue.
I do get the occasional lag in 0ad but it generally runs at 10-20 FPS. Just enough to be playable but not great, hence my desire for better performance.
My specs are Athlon XP 3200+, 2GB RAM, Radeon 9550 (AGP), Kubuntu 11.04. Runs just fine.