the problems with the attachments not working on the windows server may be with the php.ini settings. especial the timing out problem on larger files.
See the following for information on php.ini settings that can effect upload:
wap_upload.asp?page=php2
It can be done where the file is uploaded on another page, you would need to store the file name in a session variable. Then in universal email, use the session variable value for the attachment.