i would suggest you go w/ the dual core. 2 main reasons
A) there is no native quad core avaible until 2007 Q2/Q3 (so this might be possible for you if it takes that long to get a new system
)
B) the only curren methods to get quad cores are excesivly expensive (EE intel quad or AMD's solution which turned out to be a bit of a letdown)
And i would personally suggest go w/ the core 2 duo, the processors outpeform its AMD counterparts in almost every test and do so with a good margin. So unless AMD's upcoming processors are signifcantly better (and they happen to available at the time of your purchase) i personally see no reason to go w/ them outside of price (though the price/peformance curve is heavily weighted in intels favor atm)