If you want Vim to recognise files with other extensions as a certain syntax, this tip is for you. For instance, many people name their include files in PHP .inc (Coincidentally, not a very smart thing to do, but anyway). But Vim won't recognise files with the .inc extension as PHP. Here's how to deal with that:
.vimrc and add the following lines:
if has("autocmd") augroup php autocmd BufRead *.inc set filetype=php augroup END endif
This will make Vim recognise
.inc files as PHP files and treat them accordingly (syntax highlighting and whatever else you've set Vim up to do with PHP files).
Security note: It's not a good idea to name files that will be included '.inc'. Bad configuration of your webserver may make the source of those file available unparsed through your webserver. Either name them .inc.php, or don't place them in a dir under your webroot.