Wxman

Most current mobos support dual-channel these days. Mobo's that may not are those that don't have an even number of memory slots, i.e., three slots, although in that case they still may if two sticks populate the slots. Moreover, if the memory slots are color coded (with two slots being blue), this is an indicator that the mobo supports dual-channel. If single sticks populate two different color coded memory slots, then dual-channel will not be implemented. And if all slots of an odd number slot configuration are populated, then dual-channel will defacto be disabled.

The best way to determine dual-channel memory implementation/support is to look in the BIOS itself. Press DEL at boot-up, and then look in the memory configuration page. It should have an option to enable dual-channel. If its set to auto, then it'll be enabled if and when appropriate memory is found by SPD at boot time. The safest way to exit BIOS is to chose the "exit discarding changes" option (even if you don't think you changed anything).

Furthermore, it is never a good idea to mix memory timings of one's RAM. ALWAYS populate the board with identical timings. And in the case of dual channel, even pairs of similar timing & speed RAM in the appropriate slots. Memory speed is important, but even more important are the timings, e.g. 2-2-2-5, etc., you don't want to be populating the board with similar speed (but different timing) sticks of RAM. Not many BIOS have timing setups for each stick.

If you presently have 2x512MB PC2700 on the board, then you won't see much performance increase at all (unless you're doing memory intensive applicatoin use, e.g., sound, video, CAD, etc.) You may notice a performance increase if you scrap your existing 2x512 PC2700 and replace it with PC3200 (although I doubt that an 18% increase in RAM speed will be all that noticeable). However, if you run something like BOINC, that 18% will add up over time.