mod_rewrite

[eluser]Gordaen[/eluser]
I'd assume that you have an images (or similar) directory, so you could add another pipe and add that directory name. You'll definitely want to read up on regular expressions. Here's a quick explanation:

!^(index\.php|uploads|css)

! = not
^ = start of line
\. = escaping the period (otherwise a period has a special meaning and can sub in for any character)
| = or

Essentially, if the URL does NOT (!) start with (^) index.php, uploads, or css, then do the rewrite.