I can't download it, I already said. It's not the link, it's that I don't have much freedom on this computer, and downloading programs is not something I can really do.
Why can you download Texture Replacer but not Nifskope? Just wondering. Texture Replacer is a great tool for batch processing texture paths, like retexturing all cave tiles by changing 'textures\dungeons' to 'textures\MyMod' in the texture path of all the tiles for example. For changing single textures on lots of different meshes with different textures it is a pain to use though since it has a command line interface.
I'm not sure what you mean with 'doesn't it require nif files'. Of course you need the nif file you want to change, but other than that there is nothing you need for it to work.
But in the end if you want to do some serious retexturing and modding (in that regard) you will need Nifskope. If you are on your dad's computer (just a guess since I have no idea why else you wouldn't be allowed to download stuff - I hope you're not trying to mod at work) then ask him. Nifskope is not evil, thousands of people use it and there is no malware included.