FYI: It appears that 512 MB memory is insufficient if you get the GMA950 and run Vista. See post 2 in this 3 post thread:
Seeking opinions on T60 Lenovo laptop
It says, in part:
"Intel GMA 950 is chipset video with shared memory. That is not, by
itself, reason for rejecting it, this is a good, fairly powerful video
system (as mentioned, it will run the Vista Aero interface). HOWEVER,
Vista requires a MINIMUM of 512MB of SYSTEM memory, and when running
Vista/Aero on a GMA 950 system, 128MB of memory will be used by the
video system. So if you only have 512MB of total memory, your system
memory will only be 384MB, which doesn't meet the minimum for Vista
(even without Aero). Consequently, if you get GMA 950, running Vista
will REQUIRE that total memory be at least 768MB (and, in reality, 1GB
as 768MB, while physically achievable, will degrade performance by
blocking dual channel memory operation)."