I’ve been struggling at work to get .htaccess files active on my work machine (OS X server) so a litle googling provided me with an excellent blog entry on just this very topic, and within minutes I was back on scehdule.
Check out Richar Rutter’s blog entry and Clagnut .
If you are running an OS X Server you will have to be a little creative with interpreting the ‘user’ conf file with the ’sites’ conf file 
and do read the comments !