I have acquired 2 512 ram cards and have attempted to install them in my previously 256k ram computer.  when I install either by itself it works OK, but only showing 496(which someone told me why, video CARD or something.) but when I install both its like slamming windows into PARK, it takes over an hour to bring up windows, and even the little musical chime as it loads is all choppy.  Did I not resest some bios or something? 
any helpfull hints would be great, and yes I tried pulling them and reseating them after CLEANING contacts.
thanksSounds like mismatched Ram. Are both Ram sticks the same Manufacturer and specs?

Is your system Dual-Channel capable in which sticks are inserted into banks 0 and 2 when you have banks 0,1,2,3? If only a 2 bank system then this is not the issue. If inserted as 0 and 1 and dual-channel capable your system is RUNNING in single channel mode.

What motherboard or make/model computer?I'm an old diesel mechanic, so be patient with me.  I TOOK an old machine to a small shop a few years ago, he gutted it and installed a new motherboard, with a little more ram and a faster processor.  I realize all that i have now is propably out of date.
I purchased some ram from an old friend on line, I don't know if they match.
There are only 2 slots on the board for ram
Here is what it says in the properties section of my computer
system
microsoft windows xp
home edition
version 2002
service pack 2
Registered to
home
(then serial numbers I'm not sure I should give)
computer
Via Samuel 2
735MHz, 448Mb Ram
I could open system properties but that's a lot of info, what exactly am I looking for to help you help me?Trying to determine:

a) Type of RAM supported

b) Max amount of memory supported

c) max memory module size supported