I remember reading about Gtk radiant 1.5.0 on this forum, some where. Give it a search.
If you want to replace the textures of the map you have with Pb textures, copy the pball texture folder from the bsp directory and part the folder in the spot where radiant's texture directories are. As I have said before, search Gtk radiant a search on these forums and see what you come up with.
Not doing anything important in programming so I gave it a search.
This topic looks like it has some usefull information. I am unable to view the links though, due to the schools filter.