Ok, so this one only took me about 2 hours to work out. I have tried several times to email a contact item as an attachment between different versions of Outlook and usually they seem to end up unreadable or devoid of content.
In particular if you try and send a native contact item from an Outlook 2003 system to an Outlook 2007 system, Outlook 2007 will receive it as an attached message with no content e.g. no contact details. I really thought that Outlook 2007 would have been smarter than that … but I was wrong.
The secret is that you need to save/export the Outlook 2003 contact item to vCard format first and then add it as an attachment to a mail message and when an Outlook 2007 client receives it, you can save the vCard attachment as an Outlook contact.
The same issue seems to happen when attempting to exchange a contact item from Outlook 2007 to Outlook 2003, but with Outlook 2007 you can right-click on the Contact and Send Full Contact – In Internet Format (vCard) and this will work. At least you don’t need to separately save the contact into vCard format.
This doc gives some guidance http://support.microsoft.com/kb/290840
I’m sure that they could have made it easier.