Cosmos revamped their site it seems. I can't find that specific tool but this one may work too:
http://tech.wc3campaigns.com/index.php?page=downloads
Unfortunately the best part of the link in the previous posts was the BLP2Viewer which let you browse the textures without extracting/converting them. I don't think this link will help for that, tho the ability to convert non-square TGAs to BLPs sounds awesome.
edit: Oh curse-gaming is back up. Looks like someone posted the BLP2Viewer there:
http://www.curse-gaming.com/mod.php?addid=180