That's what me and tech guy had figured, but I had my doubts this morning when the major errors were coming in as memory management faults and read only memory write attempts etc, with only the occasional graphical fault.
And, after running memtest for about 14 hours, i got a single error reported.
It seems when i tried only one stick at a time of ram i forgot to swap and tested the same one on it's own twice. because now i've got the system perfectly stable with just one of the sticks in. and testing that stick on it's own through memtest i've gotten another error reported after a couple hours.
Seems amazing that what must be a tiny fault in one ram stick (Given the time it's taken memtest to find an error) could have such massive impacts, appearing as mass graphical artifacts and graphic driver failures (which was also confusing because there's lots and lots of topics on the graphic driver failing being a vista issue that has nothing to do with ram) etc.
But yes, it's one of the sticks of ram, reporting a single error in memtest every few hours or so, and causing horrible horrible problems.