|The desktop has a faster front side bus. Faster FSB=greater bandwidth between CPU and memory=higher score on memory test. |
Running a synthetic CPU test isn't the best way to determine actual CPU performance. I'm fairly certain that a 1.33GHz C2D would outperform a 2.8GHz P-D in most real-world applications.
Try encoding video with x264, Divx, or Windows Media Encoder. The C2D's extremely quick SIMD/FP unit should push it ahead of the P-D. The Core 2 also has a relatively short instruction execution pipeline, so content creation (Photoshop, Office, etc) and internet (IE, FF, Flash) performance should be right up there with the 2.8GHz Pentium D.
Socket 939|Dual-Core Opteron 185 @ 3.2GHz|A8N32-SLI Deluxe|4GB CL2 PC3200|SLI 8800GTS|1TB|PCIe X-Fi Titanium Pro|Win7 Ultimate x64