If the webhost has configured his system to listen to user configured .htaccess files, and he has allowed for the particualr .htaccess modification you're doing, then yes it will work.
Edit you .htaccess file to have the following line:
[code]AddType application/octet-stream .rar[/code]
This should make it download instead of open. You can read more about editing your .htaccess file here: application/octet-stream