How does a Intel Core 2 Duo processor at 2.40GHZ compare to a Intel Pentium 4 at 3.40 GHZ?

Answer 1

Beats it on every benchmark found on this site :
http://www23.tomshardware.com/cpu.html

Internal clock speed of a processor is not a fail proof spec for comparison purposes.
Besides having 2 cores the Core2Duo also has larger onboard cache which means it processes more data per cycle that the P4.

Not to mention that multitasking will be much much smoother on the Core2Duo.

If I had the option I would choose the Core2Duo over the P4 hands down.

regards,
Philip T