I have some old RAM lying around and I might put it in my computer. What is better for gaming? 1gb dual channel, or 1.5gb of single channel? The CAS latency and clock is the same.

It will depend on the OS, the memory management architecture of the CPU (e.g. AMD v. Intel), the mobo, the game itself, whether you're using shared video/system RAM, etc.

The best way to find out which is best fora particular instance, is to try it.

In general, the dual-channel should offer superior performance, but with just 1GB, then OS memory requirement considerations (e.g. more paging) for example, can dominate and negatively impact overall performance..

Usally 1 gig in dual channel will be better .But in some apps more ram might be better.So like John said try both ways and see whats better for your PC

We could sit here guessing at this for days. I'd test each configuration in turn with PCMARK, and possibly a couple of heavy duty games. It's the only way you're going to know for sure.

If the system needs more than 1024 MiB while running a game, the extra 512 MiB will be more useful than doubling the bandwidth. Personally, I could never tell the difference between dual and single channel but adding memory when it is needed is like day and night.

i'd say more ram.... i remember my old rig i had 1 gb ddr400 memory, and running battlefield was crap.. after i put in another 512, it was hell of a lot smoother than in the 1gb config...
also, most days today require more ram, especially with windows xp with all the updates applied to it...
i'd say more ram!