Here is what is in my working ssu install on my other website

#RewriteEngine on
#RewriteCond %{HTTP_HOST} ^mywebsite.com$
#RewriteRule ^/?$ http://www.mywebsite.com [R=301,L]

#### BOF SSU
Options +FollowSymLinks
RewriteEngine On
# Change "/zencart/ to the correct setting
# if your site is located at root folder, then you should have RewriteBase /
# Go to your include/configure.php, this value should be the same with the value of DIR_WS_CATALOG
RewriteBase /

# Deny access from .htaccess
RewriteRule ^\.htaccess$ - [F]

RewriteCond %{SCRIPT_FILENAME} -f [OR]
RewriteCond %{SCRIPT_FILENAME} -d
RewriteRule .* - [L]

RewriteRule ^(.+) index.php/$1 [E=VAR1:$1,QSA,L]
#### EOF SSU


mywebsite.com is your website url..

I am not very inclined with .htaccess files, so i dont know if the first 3 lines are even a factor in why it is working... Perhaps someone can explain it to me