I would definately use the 2 GHz Pentium Dual Core. It is based on the new “core” technology from intel and will be faster than the Celeron D, while consuming less power. Also, it is a dual processor while the Celeron D is a single core.
Hold onto the Celeron in case the dual core Pentium is not compatible right out of the box and you need to do a BIOS upgrade on the motherboard.
Go here for BIOS downloads and other updates for your mobo: