One feature that Exchange 2007 introduced is the ability to access local file shares remotely via Outlook Web Access (OWA), enabling users to download any manner of document, spreadsheet, application, etc from any machine with Internet Explorer 6 or later installed on it without having to establish a VPN connection to the local network.

Configuring the Exchange Server

File share access is enabled and configured within the Exchange Management Console. Browse to Server Configuration --> Client Access --> Outlook Web Access and open the properties for the OWA site. Different permissions can be defined for users accessing the site from Public and Private computers:

Enable the feature by ticking the option to enable Windows File Shares. The types of files that users should have access to, or not, can be defined by Customizing direct file access:

File extension types can be defined explicitly:

The details of the file servers that should be available to OWA users are defined on the Remote File Servers tab:

Click on the Block button to define those servers that should NOT be accessible. Any servers that are not explicitly blocked are automatically allowed.

The Allow list does not define those file shares that should be accessible to users, rather it defines the hosts FROM which users are connecting that should be allowed to access file shares:

As users will typically be connecting from the Internet at large, if you want your users to have access to file shares from wherever they are, the Unknown Servers option should be set to Allow rather than block.

To enable users to enter only the NETBIOS name of the file server they wish to access rather than its FQDN (Fully Qualified Domain Name), the Domain Suffix configuration allows the administrator to add any suffixes (eg 'domain.com') that should be automatically appended to any server names users enter within OWA:

NOTE - the Exchange Server should be able to resolve these domains via DNS.

Verify that the file share configured on the remote file server is configured with the correct user access permissions - ie, those users that wish to access the share via OWA won't be able to if they are not able to locally via the LAN.

Accessing the share via Outlook Web Access

Log into Outlook Web Access using Internet Explorer - the file share feature is not available from Firefox (although from looking at the Beta it looks like this is resolved in Exchange 2010). If the administrator configured different permissions for 'private' and 'public' computers, be sure to select the correct login option.
Once logged in, click on the Documents link in the bottom left-hand corner:

Select the option to Open Location:

Type in the server and share address in the form "\\server1\share"

A list of available files will be displayed:

Selecting the file will allow you to open it or save it to disk:

You can also view the file share within Windows Explorer, effectively allowing you to work from the folder as if you had mapped a drive to the share directly.
Links to files or shares contained within email messages can be selected directly (provided that they are in the correct format including the full path to the server share)

Access to remote file shares is also possible from Windows Mobile devices, provided that they are running version 6 or later of the Windows Mobile operating system. For more information on configuring this feature read this article HERE.