just to make sure, hope you are not using a graphics card that
requires 128mb of shared memory (quite uncommon, 64mb more common).
windows will only display (via control panel > system or my
computer > properties) the amount of RAM made available to the
system, excluding any such RAM which may have been allocated to
other such shared resources.
if i'm not wrong, this conclusion is made based on the assumption
(which i've learnt last time in this line) that any faulty RAM in
any slots will cause the computer not to boot up at all.
the computer will display the exact kb of RAM you have, and not in
multiples of 64Mb.