Time for an upgrade?

I'm off to college in a few short weeks. I'm bringing my homebuilt desktop system from 2007 with me and hackintoshing a dell mini 9 for a mobile computer.

My question is, do i need an upgrade yet? is it worth it, or should i wait a year or two and build a newer i7/i5 system when this one goes obsolete?

My current System:

MoBo: Asus p5n-e
CPU: Core2 E6600
GPU: EVGA 8800GTS 320
RAM: Corsair 2x1gb pc5400 ddr2
PSU: 500W
case: Raidmax Smilodon
optical drive: lh-20a1h-185
OS: vista home premium (i will upgrade to win7 come october 23)

I'm thinking of upgrading the RAM to 4gb, maybe a quad-core processor, and maybe an update on the GPU

I have a budget of up to $600, but i'd like to spend under $400, which i think is totally possible.

Should i simply upgrade RAM & save up for a replacement in a year or two?
also, can i run crossfire 4770 on that board, or am i constrained to sli configurations?

problem with an amd upgrade is that my mobo is an intel-based one, with socket 775. amd won't work unless i replace the mobo, which would almost be replacing the whole computer. if i replace any major parts, i'd like to build a cheap pc from the remaining parts and give it to my family to use. a cheap one that uses little power.

i figured that a psu upgrade was in order, i wasn't sure though. I suppose i'll look into that too.

If I were you, I'd just get 4gb of ram and get a descent heatsink and overclock the cpu. Save the rest of your money to build a completely new system when you decide you need one.

I tell you what, as someone before said: OC the cpu. Leave the rest as it is. Wait some time. Half a year or something, you'll have more cash, there will be new gpus and new cpus so even buying what you'd buy now will be half the price.