Yeap I confirm that. This implies that the problem was caused by faulted memory modules (the modules were changed) , or faulted mainboard ,or vista doesn't like 4x1gb modules , or the mainboard doesn't supply enough juice for 4 memory modules .
The problem with mem tests is that small chunks of memory are tested at a time while vista uses large amount of memory in an atomic time unit.
So , in theory , memtests does not replicate full load memory modules usage.
There is no guarantee that a memtest that does not stress all memory modules at a time can reveal if the modules are faulted.
Bottom line, test one memory stick at a time > 6hours to be sure if the module is faulted. If everthing is ok , place the stick to the ex-populated mainboard memory slots and test them one by one.
Mihai