To get to the filesystem you might use any of the following mechanisms:
Apple Filing Protocol
Install Netatalk to make your iPhone show up in Finder under Shared.
Secure Copy Protocol
Install OpenSSH to let you connect with a standard SCP or SFTP client.
iPhoneBrowser
From Windows you can use Install iPhoneBrowser from this website:
http://code.google.com/p/iphonebrowser/
DiskAid
On either Windows or Mac OS you can use Install DiskAid from this website:
http://www.digidna.net/diskaid/