Best upgrade path for a ~2 year old tower

Hey everybody,

I've come to love this site recently, and I figured you guys would be the best to ask about where the most important upgrade for my computer would be.

Long story short, I scored an amazing deal on a 2-ish year old Alienware tower through my job. It's still a very capable machine. I want to keep it reasonably current as time passes, though. When trying to figure out where to start, I got a bit snagged. Everything is just old enough to seem upgrade-ready, but I can't tell which is most important.

Here are the relevant specs:
CPU: Core 2 Duo E8400 3.0GHz
Graphics: 9800GT 512MB (x2)
RAM: 4GB DDR2 800MHz
Motherboard: nForce 680i SLI

If any other specs would be important, let me know. I don't remember off the top of my head what the power supply's wattage and other stats are, but it's quite beefy and I don't think it would impede any upgrades I'm thinking about.


Anyway, onto the specifics of my question:
I want to upgrade to two GTX 460's because I primarily use this computer for gaming, and I want to bathe in DX11 goodness. I'm not too worried about my CPU; I want an i5 or i7 eventually, but I think the E8400 can hold its ground for a while yet. I'm much more concerned about the DDR2 and the older motherboard. Will it be a "waste" of those cards in any way to put them alongside hardware that's that much older? What are some good options for an LGA 775 motherboard with support for SLI and DDR3?

In the end, the real problem is that I don't have *that* much cash on hand at any given time, and I really need to be able to upgrade my computer piece by piece, rather than in one fell swoop. I'm hoping there's a straightforward answer where I can do this in a certain order and have none of the upgrades be bottlenecked by stuff that still is hurting for an upgrade.

Thanks for any and all advice. If anything I've said is completely off the mark, feel free to correct me. I know a lot about the principles of system building but I've been away from it for a while so I'm still a little lost in the jungle of current chipsets/technologies/etc.


edit: whoops, this doesn't really belong under "homebuilt," does it? I don't see a way to change it though...