MS Outlook 2007 - need to move messages

I would like to move my old mail messages into another file (not in outlook) where they would still be searchable (like they are in outlook). There are over 20K messages in my archive folder and over 20K in my current inbox folder. These are messages to an email forum I subscribe to and I often utilize the information so I need to be able to access it, but it is slowing down my outlook and search for other items unrelated to these emails. Suggestions?