XPS 600 adding memory

The XPS 600 had four 512 sticks of memory and a 256mb video card. I removed the four sticks and put in four 1GB sticks of memory (all the same). I also swapped the video card for a 1GB video card.

Task Manager still only shows 2GB of memory. The Bios shows that I have four 1GB sticks in it. Because it is a 32bit OS, I was told it may show only 3.something GB. But it still only shows 2GB. The OS is XP Media Center. Is there something I'm suppose to run to have it update something?

I read something about adding a /3GB switch to the boot.ini file but it seems a little vague if this is a good idea or not.

CPU
Number of CPU(s) One Physical Processor / 2 Cores / 2 Logical Processors / 64 bits
CPU Full Name Intel(R) Pentium(R) D CPU 3.00GHz
CPU Name Intel Pentium D 830
CPU Code Name SmithField
Platform Name Socket 775 LGA
Revision A0
Technology 90 nm
Instructions MMX, SSE, SSE2, SSE3, ET64, XD, EST
Original Clock 3000 MHz
Original System Clock 200 MHz
Original Multiplier 15.0
CPU Clock 2993 MHz
System Clock 199.5 MHz
FSB 798.1 MHz
Core 0 Speed 2993.0 MHz
Core 0 Multiplier 15.0
Core 1 Speed 2993.0 MHz
Core 1 Multiplier 15.0
L1 Data Cache 2 x 16 KBytes
L1 Trace Cache 2 x 12 Kuops
L2 Cache 2 x 1024 KBytes

MOTHERBOARD

Property Value
Manufacturer Dell Inc.
Model 0GC375
Serial Number ..CN137405A300PM.
 
North Bridge NVIDIA nForce4 SLI Intel Edition Revision A3
South Bridge NVIDIA nForce4 MCP Revision A3
 
CPU Intel(R) Pentium(R) D CPU 3.00GHz
Cpu Socket Socket 775 LGA
 
System Slots 6 PCI
 
Memory Summary
Maximum Capacity 8192 MBytes
Memory Slots 4