@ Terroralpha: Don't talk cr**, the HS7870 isn't that far off my own 7950 and THAT can run both 2033 and LL at the high preset very smoothly, even in the demanding outdoor sections.
You're right about the memory use, though, GPUZ shows 850-900 Mb with the game at the 'very high' preset with no SSAA, even in the outdoor levels.
@ Rybo: It's not just about the GPU, both Metro games need a strong CPU, if you're using an older dual core Intel or AMD quad that is most likely to be the restriction.
Couple of points on tuning both Metro LL and Metro 2033: Don't use ANY SSAA! It hammers the frame rate and, in my opinion makes the games look worse.
Check Advanced PhysX is turned off, look in the Gameplay menu in LL! Again, this devastates the frame rate in both games for us AMD users.
The sweet spot for looks/performance is the 'high' preset, 'very high' has a heavy frame rate penalty and does little to improve the graphics.