Jeff...
I'm not sure if this will help you at all, however, I'm going to give it a shot.
I am familiar with Outlook 2000 and not 2003, but the process may, in fact be the same.
I know you copied the folder to Outlook Express, but hopefully you still have it in Outlook 2003.
Remember these instructions are for Outlook 2000...hopefully they apply, as well, to 2003.
1) Go to the folder in question...you should see all the email from this folder on your right.
2) From the Outlook toolbar, click "Edit" and then "Select All".
3) All of the email should be highlighted.
4) From the Outlook tool bar, click "File" and then "Import and Export...".
5) You should see a new window appear.
6) Where it says "Choose an action to perform:", select "Export to a file" and click the "Next" button.
7) In the next window under "Create a file of type:", select "Comma Separated Values (Windows)" and click the "Next" button.
In the next window under "Select folder to export from:", select the folder in question you want to copy the email addresses from and click the "Next" button.
9) In the next window under "Save exported file as:", click the "Browse" button and from the "Save In:" box, choose your desktop.
10) In this same window, go down to the "File name:" box and type the name you want to give this file, making sure the box underneath it also states "Comma Separated Values (Windows)" and then click the "OK" button.
11) You will return to the previous window and will click the "Next" button.
12) In the next window, make sure under "The following actions will be performed:", that it says "Export 'E-Mail messages' from the 'folder in question' folder" and that option box is checked.
13) Once it is checked...you will need to Map the Custom Fields you want to export.
14) From what I understand, you just want to copy the email addresses, but you can choose more fields if you want. There are two columns...basically, what we want to end up with is just the info we want to export in the right column...not the left. Lets say you just want the email address...drag the fields you don't want from the right column to the left column so we end up with "From: (Address)" in the right column. Again, you can leave as many fields as you want here, that's up to you.
15) Once you are done selecting the fields you want to include in the export file, click the "OK" button.
16) You will return to the "Export to a File" window...just click the "Finish" button.
The exported file will be saved to your desktop...do you remember what you named it?
That's all there is to it.
I hope you found this information useful...GOOD LUCK! Please keep us posted.