If you have the motherboard working, get cpu-z from cpuid.   That or
belarc advisor.

Each motherboard specifies what kind of memory it will accept.
DDR, DDR2 etc.   PC5300, PC2700, etc.     How big, how many etc.    Find
the specs then just search for memory then that fits that bill.
I have DDR2 PC2-4300.  If I were to want to expand, I'd search that type
and or anything my manual tells me.

However you get into manufacturers and that opens a whole new ball of
wax.   Kinston has been making chips for yeeeeeeeeeeeeeears.
But they are not the only good ones.  I have no preference.

    It is absolutely essential that any new RAM module(s) be fully
compatible with both the motherboard and/or any other RAM module(s)
already in the system.  Additionally, there are sometimes jumper
switches on older motherboards that need to be reset for new RAM
configurations.  Consult your motherboard's manual or the manufacturer's
web site for specific instructions and compatibility requirements.

    If you cannot lay your hands upon the computer's manual and the
manufacturer doesn't provide a support web site, you can use these
utilities to help determine the correct type of RAM needed:

SiSoft's Sandra
http://www.sisoftware.co.uk/index.php?dir=&location=sware_dl&lang=en

Belarc Advisor
http://www.belarc.com/free_download.html

Unlimited Possibilities' AIDA32
http://forum.aumha.org/overflow/aida32.zip

    Also, Crucial Memory's web site (www.crucial.com) has a database to
help to find the right RAM for your specific make and model computer
and/or motherboard.  (Incidentally, Crucial is the only company from
which I ever buy RAM.  I've never been disappointed.)

CPU-Z (http://www.cpuid.com/cpuz.php) is a utility that will tell you
the details of the memory that you already have installed.  That will
give you an idea of the type, configuration and speed that you need.
(It will also identify the mobo, if you don't already know it.)

Once you know that, head for the motherboard manufacturer's web site.
I think most manufacturers have a list of qualified RAM brands and
configurations for their boards.  These are parts that they have
tested and found to work.  Other brands might work or might not; you'd
be best off if you chose one of the recommended parts.

Reply-to address is real
John

Crucial System Scanner tool
http://www.crucial.com/systemscanner/index.aspx

Look at the motherboard Spec sheet.  it will tell you what it
requires.  In other words.....

Ask elsewhere