Well don't quote me on this but i'm almost sure I heard a dev say something like, if you can run mtw2 you can run empire.

Now what does this mean? I don't really know.

I'd assume this means you can play the campaign just fine, have battles just fine, and enjoy decent graphics. If you look closely you'll notice it is indeed the same engine as MTW2 so if you could get high details on that, you can get high details on this.

However as there are more animations, ai, and stuff, I'd think the question will come to unit count.
How many units can I battle with and see them awesome?

I'd say if you could run mtw2 good, probably 2k v 2k is good, 4k v 4k your limit.

If you have dual core and 2 gigs you can probably go to max.

1.5 I don't know, depends on where you buy your memory from. I mean there are diferent qualities of memory.

My advice is go to www.systemrequirementslab.com

Test your pc.

Forget whatever you bought, got sold, or made, test it. That site will show what it actually will be rated at as some things outperform (or under perform) depending on who made them.