Bad ebay Ram or uninformed newbie??

I just Ebay-bought and installed a 2 gig exactly matching Samsung stick into SL510 with one OEM 2 gig stick, oddly made 8 days before the Ebay stick. The used Ebay stick was shipped to me without any padding, just bouncing around in a little cardboard post office box. I'm running Windows XP 32 bit which I'm told can see 3.5 gig of memory.

Lenovo Toolbox sees 4gig 2 Samsung 2 gb sticks with all the serial numbers, etc
Control Panel/System Properties/System Info says ONLY 2.83GB ram
Windows Task Manager says
Physical Memory
Total 2978596
Kernel Memory
Total 157832

I've searched here, but frankly don't understand the answers.
Does my new/used stick seem to be working properly?
I have to stay with Windows XP 32 because of old software that won't run on Win7 32 bit or 64 bit.
What can I do to get the laptop to utilize up to 3.5 gig

 

what you're seeing is 100% correct.   32-bit windows desktop OSes can only address ~3GB total.   to say this topic has been beaten to death would be an understatement.

you'd need the x86 version of server 2003 or 2003 R2 to utilize 4GB under an XP-based 32-bit OS.   it's technically a 36-bit OS and supports memory hoisting, allowing the last 1GB to get out of its own way and free the address space.

XP 64 might also work for you if your software can run in a WoW (windows-on-windows) environment.   despite being able to function, not all software will install on XP64 due to complaining about the OS version.