According to Dell's website these are the only processors your motherboard can use and IMO none of them are really worth spending the mone on.
Intel® Pentium® 4 processor that runs at 2.8 GHz , 3.0 GHz, and 3.2 GHZ internally and 800 MHz externally with Hyper-Threading Technology
Intel Pentium 4 processor that runs at 2.8 GHz internally and 533 MHz externally
Intel Celeron® D processor 320, 325, 330, 335, and 340