I did this on a PC, and yes it did work. PC3200 should be backwards compatible with PC2700 when used with it. However, I had to play around with the BIOS settings to make it work...and it did...until the power went out and the PC didn't want to boot. The difference between the dual channel memory and the single channel memory caused it not to function properly. I had to pull out the one of the modules for the PC to boot up properly. Having one or the other installed allowed it to boot, but neither played nice with one another.
So my answer from experience: you can mix it, but be ready to encounter problems along the way.