If you need to run the script client-side, you will probably have to use a cgi (which would actually run on the server anyway) unless you use mail-to, because client-side you would be using the viewer's email (like Outlook, etc.)
If you need a simple script, you can run it server-side on as asp page using CDONTS, something like this:
var objNewMail = Server.CreateObject("CDONTS.NewMail"

;
objNewMail.BodyFormat = 0;
objNewMail.MailFormat = 0;
var strBody = "<html>";
strBody = strBody + "<head>";
strBody = strBody + "<meta http-equiv='Content-Language' content='en-us'>";
strBody = strBody + "<meta http-equiv='Content-Type' content='text/html; charset=iso-8859-1'>";
strBody = strBody + "<title>Mail message</title>";
strBody = strBody + "</head>";
strBody = strBody + "<body>";
strBody = strBody + "<p><font face='Arial' size='2'><u>body text here</u></font><br>";
strBody = strBody + "</body>";
strBody = strBody + "</html>";
objNewMail.Body = strBody;
objNewMail.From = "someone@somewhere.com";
objNewMail.To = "someone@somewhere.com"
objNewMail.Cc = "someone@somewhere.com";
objNewMail.AttachFile = "c:\filename.txt";
objNewMail.Subject = "subject";
objNewMail.Send();
objNewMail = null;
Your server has to be set up to work with CDONTS.
Of course, if your attachment is coming from the client, that's different, and you are back to using a cgi.