I have an Apache 2 server running perfectly on Fedora Core 2, with mod_rewrite working too (and I know it works cos my blog uses it)

I am hosting some maps for a counter-strike server on a free webhost on the internet, because it's faster than my server. I want to be able to use this server as a download location for maps on my game server. However, the webhost don't allow the filetype of the maps

What I want to do is use a mod_rewrite rule on my server to do the following:

I request file:
http://mysite/cstrike/maps/de_train.bsp

I want that to actually down the file as:
http://externalsite/cstrike/maps/de_train.bsp.txt

BUT: I need the file to come as a BSP file, not a TXT file.

It's a strange situation I know, and I'm not sure if i can do it with mod_rewrite but I think it's possible, I just don't know how!

Please if anyone has ANY ideas just say!