I would like to be able to split my preferred browsers in Windows XP so that IE opens some sites (external), and Firefox opens all others (internal).
Is there a way to do this in Windows XP?
You can use Firefox as your main browser and install the IE Tab Plus add-on (formerly Coral IE Tab).
This add-on allows you to define URLs for which IE will be used, you will then get a new tab which uses IE for rendering the page.
Works fine for things like http://update.microsoft.com/ or the Outlook Web Interface.