"WINMAIL.DAT is a proprietary Outlook file that allows Outlook users to send Transport Neutral Encapsulation Format (TNEF) information (see Microsoft's technical support article at <http://support.microsoft.com/support/kb/articles/Q241/5/38.ASP)>. This TNEF information is unopenable and irrellevant outside of Outlook.
Your real problem is that AOL is notorious for trashing attachments, especially ones that are larger than 1MB.