hannoes, it should work out of the box. Have you tried publishing the site through RapidWeaver and trying out the contact form? You may need to tweak some settings in the site's configuration in RapidWeaver to reflect the correct From address; it should be
name@
yourusername.x10hosting.com (unless you've selected an alternate domain, such as exofire.net, in which case you'd need to provide that in place of x10hosting.com).
--- Mr. DOS
Edit: For general reference,
RapidWeaver is a piece of Mac OS X-only software that allows easy creation of mostly-static sites. It's basically an offline CMS. It also comes with a few scripts, such as the PHP mailing script in issue here. (Other scripts can also be added in later through plugins, I believe; it's been over a year since I had to use RW and I was only doing theming then.)