WHAT KIND OF RAM DO I BUY FOR MY MOTHER BOARD-845 G MAX (MS-6580 VER:
10 A).  I WANT TO GET 512 MB  UPGRADE . I HAVE A PENTINM 4 2.4 GHZ.
RIGHT NOW I HAVE 256 RAM WITH 2  MORE SLOTS AVAIABLE.  I HAVE A 60
GIGABYTE HARD DRIVE

Hello.

The 845G MS-6580 motherboard uses 184-pin DDR SDRAM DIMMs (2.5 volts).

From MSI, the manufacturer of your motherboard, the board has:
"three 184-pin DDR DIMM sockets."
http://www.msicomputer.com/product/detail_spec/product_detail.asp?model=845G_Max_L

Also see "MSI MS-6580  Mainboard" manual:
http://download.msi.com.tw/support/mnu_exe/E6580v1.0.exe
From pages 2-5 & 2-6 of the manual:
"The mainboard provides 3 sockets for 184-pin DDR SDRAM DIMM (Double
In-Line Memory Module) modules and supports the memory size up to 2GB.
You can install PC2100DDR266 or PC1600/DDR200 DRAM modules on the DDR
DIMM slots (DIMM 1-3).

Inroductions to DDR SDRAM
DDR (Double Data Rate) SDRAM is similar to conventional SDRAM but
doubles the rate by transferring  data twice per cycle. It uses 2.5
votes as opposed to 3.3 votles used in SDR SDRAM, and requires 184-pin
DIMM modules rather than 168-pin modules used by SDR SDRAM. High
memory bandwith makes DDR an ideal solution for high performance PC,
workstations and servers."
Source: MSI MS-6580 Mainboard manual, pp 2-5 & 2-6, hosted by
MSI.com.tw:
http://download.msi.com.tw/support/mnu_exe/E6580v1.0.exe

Here are a couple of lists of dealers for PC2100 DDR 512MB DIMMs
PriceWatch: PC2100 DDR 512MB
http://www.pricewatch.com/1/33/2841-5.htm
Deal RAM: PC2100 DDR SDRAM DIMMs
http://dealram.com/prices/11/512MB.html

search strategy:
msi.com, 845g, manual
pc2100 ddr 512mb

I hope this helps.