I don't really understand the importance of a motherboard... so if someone could ELI5, that would probably help. :D Anyway, my PC sits around doing nothing because my laptop has better performance than it, so it's time to upgrade. It's using an 8800GT and an AMD AthlonT X2 5200 Dual-Core CPU right now. :-/ The motherboard is:

Asus M2N-SLI NVIDIA nForce 560 SLI Chipset w/7.1 Sound, Gb LAN, S-ATA Raid, IEEE 1394, USB 2.0, Dual PCI-E MB

What's the best graphics card/processor I could get for it? I have a 600 watt power supply, so I should be able to get something decent, but maybe not SLI. Do I need a new motherboard? Would it really hold me back to keep it?

Thanks. :)

EDIT: Okay, so it looks like my limiting factors are only having PCI Express (1.0?) and AM2/AM2 available. So, a better question might be: what's the best I can do with PCI Express x16 and AM2/AM2 ?

EDIT2: Found out that PCI Express 2.0 and 3.0 are backwards compatible with 1.0! Woo!

EDIT3: Further investigation showed that the best processor I can get with my mobo is an AM3 socket, so that will really be my limiting factor. Thank you for the responses guys.