mod-rewrite

I have just started using mod-rewrite, and have two questions... I see everywhere on the net that I can change file names to lower case - at present they are an ex-Windows based mess of upper and lower. But I can't see anywhere how to actually do it, just that it is possible. Also, I use RewriteRule ^comm/(.*).php /comm.php?C=$1 to change comm.php?C=abc to a more search engine friendly comm/abc.php. But this leaves gives the effect of being in a different folder, and relative URLS within that page no longer work correctly. Is there a Clever Fix? Or do I have to change to absolute URLS? And if absolute is absolutely necessary, should I include the domain name? -- Pete Clark