I imported these rocks from an old 3dsmax render I had on my PC to nifskope for use in the upcoming Skyrim for Oblivion mod. Unfortunately, they don't show up ingame, though they appear fine in nifskope. I haven't tried generating collision yet, but I don't imagine thats the problem. I've never had this sort of a problem with Nifskope before.

Could someone take a look please?

http://www.filefront.com/16623719/Rocks.rar

Thanks!

That's one of those typical errors ;]

You have two main NiNodes in your nif - NiNode (0) and NiNode (1) and NiNode (0) is empty. While Nifskope can render all main Ninodes, the game's engine on the other hand uses always first main NiNode (0) only. The other main NiNodes on the same level are discarded by the game.
You need to copy/paste branches from NiNode(1) to NiNode(0) and delete unused NiNode(1).

Could I just delete NiNode(0) so NiNode(1) was the main one?

And BTW Thanks trollf!

Yes, you can try that. As NiNode(0) is empty anyway, all should work after you delete it.