Outlook 2003 does not have "Identities".
What it does have is profiles.
You can create a different profile for each of you.
Outlook Express can export messages to Outlook.
It does not give you a opportunity to select the profile that you want to
export to and instead just exports the what ever profile is set as default.
You will need to do this similar to the following.
Create a Outlook profile for each of you. (you and your wife)
Set Outlook to use your default profile.
Open Outlook Express to your identity and export the messages to Outlook.
Once this is completed.
Change the default profile for Outlook to your wife.
Open Outlook Express to your Wife's identity.
Export the messages from Outlook Express.
OR
Follow the steps in the following article on how to Import message from
Outlook Express.
In your case you will need to maintain two profiles in Outlook, one for
each of you.
OL2002: How to Upgrade from Outlook Express to Outlook 2002 WGID:220
ID: 291602.KB.EN-US
http://support.microsoft.com/?id=291602
Tammy