Running > 4GB of Memory

[Mark Hansen <mark@javector.com>]

I'm running debian on a dell poweredge 1750 and just intalled 6GB of 
memory.  Its a dual-processor machine and I use it with VMWare to run 
multiple virtual machines.

Problem - I can only "see" 4GB of memory.  Here is the output from
"free -m":

mhansen@debian01:~$ free -m
             total       used       free     shared    buffers     cached
Mem:          3995       3908         86          0        145       2668
-/+ buffers/cache:       1094       2901
Swap:         2047          0       2047


What do I need to do in order to make the other 2GB of memory available?

Thanks,

Mark