Not sure that this will work, but you can give it a try. Add the lines in red, to inc_mail.asp, in the Cdosys code area:
objNewMail.To = strRecipients
objNewMail.From = strSender
objNewMail.Subject = strSubject
objNewMail.TextBody = strMessage
Set bp = objNewMail.BodyPart
bp.Charset="windows-1251"