Question : Problem: Intel Core 2 Duo or Intel Pentium D945?

I am about to purchase a number of new machines and I am weighing up the benefits of the Intel Core 2 Duo (E6xxx) versus the Intel Pentium D9xx range of processors. The machine I will be purchasing is likely to be the HP DC7700 SFF chassis, but I would like to better understand the benefits of both processors.

The machines will be running Windows XP Pro (32 Bit), Microsoft Office 2003 and also a combination of Bloomberg and Reuters 3000 Xtra (financial applications).

The processor choices I am looking at are the E6400 vs Pentium D945.

Answer : Problem: Intel Core 2 Duo or Intel Pentium D945?

"... I am weighing up the benefits of the Intel Core 2 Duo (E6xxx) versus the Intel Pentium D9xx " ==> The "go with the Core 2" conclusion that you should reach has been pretty well stated; but I thought I'd summarize the reasons for that:

Benefits of D9xxx series:  Possibly a small price advantage;  4MB of L2 cache vs. 2MB for the E6400.

Benefits of Core 2 Duo:   Less power (thermal design power 65w vs. 95w);  runs cooler (because of the lower power);  Appreciably faster [not "double" as stated in a previous comment (except in very select benchmarks);  but nevertheless ~ 50% higher SYSMark; 20% higher PCMark; etc. => there is NO benchmark I've seen where the E6400 does not beat a D945];  improved cache algorithm and shared cache [the Pentium's 4MB of cache is 2 x 2MB;  the E6400's 2MB is shared between both cores].

"... I would like to better understand the benefits of both processors ..." ==>  Both are dual-core CPU's, so provide the benefits of having dual processor cores.   But in virtually all other aspects (except cache size, as noted above), the Core 2 Duo is superior to the Pentium D945.   I like this quote from the last page of an Anandtech article last summer ... just after the Core 2's were released:  "... In one day, Intel has made its entire Pentium D lineup of processors obsolete."   That pretty much sums it up ... and should make your decision very simple :-)