I like PHP.
You'll want to check the PHP manual in the
file_upload section. There are a couple of simple examples you can use straight away.
Things to keep in mind: Your form MUST use the "multipart/form-data" encoding, you MUST have a directory in which to store the uploads that is writeable by your web server user identity (apache, nobody, etc.), and you simply MUST take whatever security steps are suggested to protect your server ... unless you WANT to become the unwitting host of pirated copies of Windows Vista and any type of porn you can imagine ...
<edit>
Oop! You'll also want to check out the PHP maual section on the
mail function. A note regarding attaching the file: You can grab the MIME-type of the uploaded document during the upload procedure ($_FILES['userfile']['type']) to use during mailing.
</edit>