I am not sure about Hotmail, but if you check Yahoo E-mail HELP, and look for export/import you get the following directions for exporting your address book to Outlook Express:http://help.yahoo.com/help/us/ab/impexp/impexp-12.html
"First, export the information from your Yahoo! Address Book:
1. Open your Yahoo! Address Book and click "Import/Export" in the upper-right corner.
2. In the Export section, click "Export Now" next to the phrase "Microsoft Outlook."
3. A dialog window opens and gives you the option to save your Yahoo! Address Book to disk as a .csv file. Click "Save to Disk".
4. Click "OK". The .csv file will be saved to your desktop.
Next, import that file into Outlook Express:
1. Open Microsoft Outlook Express.
2. Select "Import" from the "File" menu.
3. From the "File" menu, select "Other Address Book."
4. Select the file type "Text File (Comma Separated Values)."
5. Click the "Import" button.
6. Enter the location and name of the file you exported from Yahoo! or use the "Browse" button to find the file. Then click the "Next" button.
7. Check the fields you wish to import, and uncheck any fields you do not wish to import to Outlook Express. Or, click "Change Mapping..." to modify where to store the data from Yahoo! Address Book in Outlook Express.
8. Click "Finish" to import the data."
I suspect that Hotmail will have similar instructions, although the precise format of the exporting file may differ in their case.
An alternate way to add them to your OE address book (and edit the list at the same time) is to simply tell OE automatically to add anyone to whom you reply to the address book.
Hope this helps,