E7500 - Core 2 Duo - 45nm Wolfdale CPU @ 2.93 GHz and 3MB of L2 cache released in Jan. 2009.http://ark.intel.com/products/36503/Intel-Core2-Duo-Processor-E7500-(3M-Cache-2_93-GHz-1066-MHz-FSB)
E5700 - Pentium - 45nm Wolfdate CPU @ 3.00 Ghz and 2MB of L2 cache. Released in Aug. 2010.http://ark.intel.com/products/42801/Intel-Pentium-Processor-E5700-(2M-Cache-3_00-GHz-800-MHz-FSB)
The Core 2 uses a 1033Mhz bus while the Pentium chip uses an 800 Mhz bus for the memory, that and the L2 cache will be the major differences. Realistically though I'd buy whichever is cheaper as real world performance will be nearly identical (even benchmarks are nearly the same for these two).
EDIT: Just noticed you specified E7400 not E7500...
E7400 - Core 2 Duo - 45nm Wolfdale CPU @ 2.80 GHz and 3MB of L2 cache released in Jan 2009.http://ark.intel.com/products/36500/Intel-Core2-Duo-Processor-E7400-(3M-Cache-2_80-GHz-1066-MHz-FSB)
Same conclusion though. maybe a slight edge the Pentium chip.