Are you running Repos Style directly from a subversion repository?
That probably explains the problems with repos.xsl mime type in our
last thread. You solved it using ModMimeUsePathInfo but svn propset
would probably have worked too.
Running php from subversion is more tricky because apache has the
concept of handlers, and runs either mod_dav_svn OR mod_php. Xsl is
easier because it can be served using any handler and let the browser
do the transform. With php this is not really supported, but I have a
vague memory of someone reporting to the mailing list something like
this. Have a look through older posts.
/Staffan