According to the Intel website, it would work. The following is taken from their website:
Rules to enable dual-channel mode To achieve dual-channel mode, the following conditions must be met: Same memory size (1 GB, 2 GB, 4 GB, etc.) Matched DIMM configuration in each channel Matched in symmetrical memory slots Configurations that do not match the above conditions will revert to single-channel mode. The following conditions do not need to be met: Same brand Same timing specifications Same speed (MHz)
Source: http://www.intel.com/support/motherboards/desktop/sb/cs-011965.htm
Personally, however, I would much prefer to have the exact same ram in each slot. If this isn't an option, it should work though. Hope this helps.