We got this tip from one of our colleagues; it activates server access using the “Documents” button on Outlook Web Access.
First, configure Remote File Access in Exchange 2007 in the Exchange 2007 MMC. It's described here.
To specify the servers users have access to, go to Server Configuration –> Client Access. In the Actions panel on the right side of the window, click on properties below OWA.
Next, click on the Remote File Servers tab and click the Allow button. Enter the server name to be accessed and click the Add button. If desired enter the SharePoint server name as well. For any server name entry, just enter the name of the server (no FQDN, no slashes).
Click OK, click Apply and then OK and close the Exchange MMC.
In OWA, open the location using the format file://server/ or for SharePoint, use http://sharepointservername/documentlibraryname. Once the files are displayed, you may want to save the location in the Favorites list on the OWA Documents page.