If user receives .DAT attachments then it is due to the fact that .dat file is used to preserve the formatting of email when email is sent in RTF format. Outlook creates .dat file not WORD so we cant really blame word for just ticking one option in outlook "Use MS Word as email editor". We can use WORD to send emails HTML and plain text format. As also explained in following article.
http://support.microsoft.com/kb/278061
http://support.microsoft.com/kb/138053/
When you talk about security holes and exploits then why to use Outlook as it is also a MS product and has got issues with security and bugs (as explained earlier). If we keep our MS products up to date and make ourselves aware of forthcoming threats then we can avoid (not vanish..:-)) the threats.
Regarding my company, I will not discuss how we are securing our back doors and keeping our systems secure... :-) There are reasonable possible ways that you can implement to secure the system without blaming the products that you use in professional environment.
Anyway, I am happy that problem is solved and I have learn from others experience.
Cheers !
Keep Sharing Knowledge...:-)