So, I installed 2.49b version, because apparently that's the latest version the .nif plugin would work with. The problem is, everytime I try to run the plugin, I get the message saying that it cannot find PyFFI.

Thing is, I did install PyFFI. The console says to bring it to blender's script folder. I did. Nothing works. It also mentioned Python's folder, which I did bring it to. Still didn't fix the problem.

I had this problem myself, try installing PyFFI again, don't know if it will work for you, but in my case it did.

Follow the directions in the linky below, on what to install for Blender (except read my notes further below, first):
http://www.tesnexus.com/downloads/file.php?id=12248

The part where the above linky says:
"(The version 2.49b download (Blender 2.49b, Python 2.6.5, Blender NIF Scripts 2.5.5, NifSkope 1.0.22, PyFFI 1.1.5) is the currently "accepted" version and contains all related files and versions known to work well together.)"

You actually should download:
Blender 2.49b, Python 2.6.6, Blender NIF Scripts 2.5.7, NifSkope 1.0.22, PyFFI 2.1.9)...but still follow the order of installation in the TesNexus link above.

I hope this helps.

Koniption