As for CPUs, the chart is quite simple: Socket-whatever processors run in socket-whatever mainboards, and nowhere else.
On socket-939 and -754 (the current platforms), any DDR RAM from PC1600 to PC3200 is good. Faster doesn't help unless you'll be overclocking, slower DDR standards don't exist. Socket-939 is a dual-channel platform, and hence wants matching pairs of DIMMs.
On socket-A, the valid combinations between CPU front side bus and RAM bus frequency largely depends on the chipset the mainboard uses - some are wildly flexible, some aren't.