You can import .nif files into Blender 2.49, but it will take a little editing of the nif files to get it working.
First you need to open a .nif file in Nifskope (I use 1.1.3). When done loading go down to your block details and expand NiHeader. There you see the variables 'User Version' and 'User Version 2', which have the values 12 and 83. You'll need to change these to 11 for 'User Version' and 34 for 'User Version 2'. Save the nif-file as a new file somewhere and open it again in Nifskope.
Now you'll have to do some cleaning to get the importing working, as not all branches will work in Blender.
Open the branch you see and expand everything. You'll need to remove everything except NiNode, NiTriShape and NiTriShapeData and the parent nodes of them. You can do this by right-click > Branch > Remove Branch or selecting the branch and pressing Ctrl + Del. Most of the time you'll only need to remove BLightingShaderProperties, BSShaderTextureSets and bhkCollisionObjects.
Save your file, open up Blender 2.49 with the scripts (I take it you already have them installed, else look in the tutorial below). Import the nif-file and start editing.
It is a lengthy process and I cannot write down everything so I suggest taking a look at some tutorials. This one is the most detailed I could find:
http://wiki.tesnexus..._Skyrim._Part_1