Questions on laptop specs

Hi everyone. I'm about to buy my first laptop and after hours of grueling research I've finally decided on the HP HDX18t. However, there are some loose ends that I still need to tie up with some definitive answers. I'm looking to use this laptop for some serious gaming (WOW, HL2, etc) entertainment (Blu ray movies, music), schoolwork, and need it to last throughout my time in college while still being technologically relevant.

First, I'm split between two processors for my laptop listed below:

Intel(R) Core(TM)2 Quad Processor Q9000 (2.00Ghz, 6MB L2 Cache, 1066MHz FSB)

Intel(R) Core(TM)2 Duo Processor T9900 (3.06 GHz, 6 MB L2 Cache, 1066MHz FSB)

I've heard that quad cores are the future of gaming etc and that they perform better than dual cores, but looking at the overall clock speeds, and the fact that it's not easy to overclock laptop compenents I was wondering if the dual core will end up providing more bang for the buck. The dual core is also $100 more expensive.

Second, should I be load up on DDR2 memory or invest in DDR3 memory. It seems that DDR3 is becoming more mainstream so it may be best to align my graphics card accordingly. However, DDR2 still remains the more economical choice, I'm looking to add around 4 gigs either way. (As a side note, is 4 gigs enough or should I go higher).

Third, they are giving me the option, at the same price to choose between 2 500 gig hard drive configurations:

500GB 7200RPM SATA Hard Drive from 320GB 7200RPM SATA Hard Drive

500GB 7200RPM SATA Dual Hard Drive (250GB x 2) with HP ProtectSmart Hard Drive Protection

Is there any benefit to dual hard drives and are there drawbacks. I'm assuming to operate two drives at once the dual configuration would draw more power and battery life from the laptop (this is just a guess). Since they both operate at 7200 rpm would this make a significant difference in terms of speed.

Lastly, I'm planning on adding the 1GB Nvidia GeForce GT 130M graphics card, is this sufficient to meet my needs listed above or should I be looking elsewhere.

Thanks in advance for your time.