Force WWW with htaccess

[vBNinja]

hello


i want to force www on my forums so that if its typed without the "www" it automatically adds it

my forum not on the main domain, it is a subdomain so the code needs to be made to work within the directory where my forum is on

my forum is in a directory called "forums"

so basically: http://mysite.com/forums

i want everything within the that directory to automatically get the "www"

Can someone please help me


Thank You