Change yourdomain.com to be your main domain

[Gavinmorrison]

Please help guys and girls

Ive installed vbulletin onto my host and all is working fine however im trying to make my vbulletin site appear instead of the phpbb forum.
Monstor have advised to do the following

# Hostmonster.com
# .htaccess main domain to subfolder redirect
# Copy and paste the following code into the .htaccess file
# in the public_html folder of your hosting account
# make the changes to the file according to the instructions.

# Do not change this line.

RewriteEngine on

# Change yourdomain.com to be your main domain.

RewriteCond %{HTTP_HOST} ^(www.)?yourmaindomain.com$

# Change 'subfolder' to be the folder you will use for your main domain.

RewriteCond %{REQUEST_URI} !^/subfolder/

# Don't change this line.

RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d

# Change 'subfolder' to be the folder you will use for your main domain.

RewriteRule ^(.*)$ /subfolder/$1

# Change yourdomain.com to be your main domain again.
# Change 'subfolder' to be the folder you will use for your main domain
# followed by / then the main file for your site, index.php, index.html, etc.

RewriteCond %{HTTP_HOST} ^(www.)?yourmaindomain.com$
RewriteRule ^(/)?$ subfolder/index.php [L]

But im really usure how to do this can anyone help

Thanks