I don't why it wouldn't be. I was using MBL when I had a 7900GT on a single core processor. Now I run Dual Core with 9800 cards, but an 8400 should do the trick.
i have the 8400...exact one you reference...works fine on my dual core sys...only issue is when i try to preview at full quality in my timeline, it's a tad jumpy, so not a big deal.