In Windows 7, if you want to do a true multi-monitor remote desktop session, both the local and remote machine need to be running Windows 7 Enterprise or Ultimate. If you're using a different version, you can still span the remote desktop session across all of your monitors, but it will be treated as one large display. Using DisplayFusion, you can split that spanned session into smaller virtual monitors.
The steps below assume that you have two monitors of equal screen resolution on your local machine (the machine you're connecting from). If you have more than two monitors of equal screen resolution, just make sure to setup the splits in step 5 appropriately (i.e. 3x1 for 3 monitors).