Is it true that Core duo Macbooks won't run Leopard as

Leopard will be BOTH 32 and 64 bit binary. I believe that the installer DVD will install the appropriate resolution operating system for the CPU it is being installed for.

Given your or most anybody's needs, I don't think there's anything at all to worry about. The only speed impediment I see occurring running 32 bit Leopard on a 32 bit Core Duo -- or even a G5 for that matter -- will be YOUR knowledge that you didn't buy a Core 2 Duo In the vast majority of usage scenarios, 64 bit will matter to a small segment of the userbase such as media production. As Lars pointed out, of course a 64 bit system will run faster, but you won't notice it doing internet-based, office-based or consumer-based multimedia functions.

The important thing with ANY modern OS is ensuring you have a MINIMUM of 1GB of RAM, and that used system you're looking at would choke up on Tiger let alone Leopard with only 512MB of RAM once you were running even just a few apps. The performance difference between 512MB and 1GB of RAM on my 1st gen G4 Mini was significant.