problem with games

ok im haveing a problem with high speed games EX.(call of duty 4) if i run the game at any thing more than min. graphics settings the game runs for a short time then system closes out and restarts and i get a message saying memory exhausted so i decided well easy fix ill just put in a few more mem. chips to fix the problem. well while checking out mem chip sets i found a set of chips for pretty cheep cheeper than the stock set in the system now i listed it below.
Memory Size: 1024MB
Memory Speed: 800MHz PC6400
Memory CAS Latency: 5-5-5-12
Memory Type: DDR2
Pins: 240
but my system came with ddr2 x2 1024MB 533MHz PC4200.
can i use PC6400 and PC4200 at the same time or just one type at a time?
and if i did change all over to the PC6400 would that give me any advantages over useing the PC4200 because of the 800mhz vs 533mhz or will the system not use full advantage of the ex. MHz with out overclocking the FSB? (this is with out overclocking my system just mem change) well if anyone can answer this question it would be a lot of help thnks!

heres my system specs:

gateway gm5260

Processor: Intel® Core™ 2 Duo E6300 (dual core) 64-bit processor
Each core operates at 1.86 GHz
1066 MHz front side bus
Shared 2 MB L2 cache

Memory Installed: 2048 MB DDR2 (PC4200), 533 MHz memory (two 1024 MB modules)
Expandable to: 8 GB (4 memory slots)

Video No integrated video solution
NVIDIA GeForce™ 7300LE Turbo Cache, 64 MB video add-in card with VGA, DVI, and S-Video ports
Up to 256 MB with shared video memory

Audio Integrated 8-channel (7.1) High Definition Audio
Hard Drive 320 GB, 7200 RPM, Serial ATA II hard drive with 8 MB cache
Optical Drive DVD +/- RW, 16X multi-format double layer drive (up to 8.5 GB)
Write max: 16X DVD-/+R, 6X DVD-RW, 8X DVD+RW, 4X DVD+R DL, 40X CD-R, 24X CD-RW Read max: 16X DVD-ROM, 40X CD-ROM

Media Reader 9-in-1 Digital Media Manager supporting the following:

CompactFlash Card
IBM MicroDrive
Memory Stick
Memory Stick Pro
SmartMedia Card
Secure Digital(SD)/MMC
Compact Flash
Multimedia Card
xD-Picture Card
USB 2.0

Modem 56K ITU V.92 ready Fax/Modem
Network Integrated Intel 10/100 Mbps Ethernet LAN
TV Tuner TV tuner card with one TV coax port, two RCA stereo audio jacks, one RCA video jack, and one S-Video port
Interfaces PS/2 keyboard port
PS/2 mouse port
Nine USB 2.0 ports (six on rear panel, two on front panel, one in media reader)
Two IEEE 1394a connectors (one on rear panel, one on front-panel)
One RJ-45 LAN port
Seven audio jacks (five on rear panel, two on front panel)
One S/PDIF digital audio out port

One internal serial connector on motherboard
One internal parallel connector on motherboard

Add-In Card Slots One PCI Express ×16
One PCI Express ×1
Two PCI Conventional

Drive Bays Two external 3.5-inch
Two external 5.25-inch
Two internal 3.5-inch

 

Re: problem with games - - - PC 6400 RAM chips

Did this up grade in faster, pc6400, RAM help with your gaming on your GM2560?
I ordered 4 gigs of 6400 RAM, or am about to.
Thank you,
S

 

Oh, and also have you upgraded your Video card on you GM5260?