Judging from your code, you appear to be running on http://www.hypermart.net. On their site they say they have Mailtools and Mime-Tools installed for paid users. MIME::Lite is included therin, and should take care of everything you need, and if not, those packages include more advanced tools. (I haven't used Mail::Sendmail recommended by others, but Mail::Mailer is included in Mail-tools and has gotten very good comments from others on this site.
in reply to allowing form uploading
All the comments mentioned here (and those in reply to you previously at Dangers of rolling your own mail script) apply, so I recommend using one of those modules, particularly for something as sticky as attachments.