You don't say what you've placed in your .htaccess file, but here's a copy of what's in mine that does the same thing. Note that I've got a bit in there so that my .htaccess works properly when I'm in my testing (i.e. localhost) environment, too:
Code:
# If the request comes in as smellsonice.co.uk, add the www. prefix
#
RewriteCond %{HTTP_HOST} !(^www\.smellsonice\.co\.uk$|^localhost$) [NC]
RewriteRule ^(.*)$ http://www.smellsonice.co.uk/$1 [R=301,L]
P.S. If you're really still on v1.3.7, you really, really need to upgrade!