No. DDR3 and DDR2 are designed differently. Both have different key placing so they won't even physically fit, not to mention differences in electrical voltage:

alt text http://kadakam.files.wordpress.com/2008/12/ram_kadakam.jpg

There are motherboards which will provide entirely separate slots for DDR2, but you cannot use DDR3 in DDR2 slots, or both types together.

No. DDR3 and DDR2 are designed differently. Both have different key placing so they won't even physically fit, not to mention differences in electrical voltage:

There are motherboards which will provide entirely separate slots for DDR2, but you cannot use DDR3 in DDR2 slots, or both types together.