thats not the max it can use, thats just what its using RIGHT THEN.
try combining the used and the available to figure out how much you CAN use, i can almost gaurantee its below 4gb, since 4gb ram is not used effectively in Windows XP, a lot of it is just wasted.
for a while i had 4gb ram, and a system report told me i only had 2.3gb available ram, because windows XP doesnt know what to do with the rest, since its not built for ram that high.
if you want more ram support, get windows server 2003 or x64
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