Actually, TXI's are texture functions. Just little text files which tell the engine how the texture should be manipulated while being displayed. To associate a TXI with a texture, just give the TXI file the same name as the texture and it will automatically be loaded and acted upon.
So if your texture is
foo.tga or
foo.dds, your TXI will be called
foo.txi.
When a texture has an accompanying TXI, every model which uses the texture will also display it with the TXI settings you added. So it usually helps to give the texture and TXI unique names so that you don't accidentally affect other models using the same texture. (e.g. mytex.tga & mytex.txi)
Great way to find a good TXI for your texture is just to find another piece of custom content whose textures have the same effect and copy and rename the TXI they used.
But is a TXI going to help your issue? I'm not so sure about that. If it displays on one machine fine but not on another, and if everything on both machines is the same hak & file wise then sounds like a display driver issue or something else, not the actual content. Never hurts to post screenshots, BTW.
'> You can google around and find lots of threads on the old Bioware forums about driver issues regarding transparency and recommendations on the most NWN-friendly drivers.