Mixing RAM memory?

I have a desktop with three 164-pin memory slots (yea, old shit i know) with one 512MB stick on it, and I've been playing games for a while with this royal turd.  I'm getting sick of this, so I'm thinking about getting some dirt-cheap memory off Ebay and sticking it in along with my 512MB.  The model's will not match, and I'm planning to fit all three slots with two 256MB, and my current 512MB.  Will this work or should I just kill myself for my computer failure?

Why waste money on expensive old RAM, when you can apply that money towards an upgrade to a more modern CPU/mobo/RAM platform?  As you're browsing for your 168-pin DIMMs, just know that you could get an AMD 64-bit CPU, AGP-compatible mobo (to keep an old video card or use current ultra-value cards), and 2 GB of Micron DDR2-667 dual-channel RAM for around $110 final cost, based on some deals going on in the U.S. right now.

>>3
I can't remember any situation or RAM type where you had to pair off SDR/168-pin DIMMs.  I remember pairing off SIMMs, RIMMs, and DDR/DDR2 DIMMs for dual-channel, but never 168-pin.