There is no difference between local and network scanners in TWAIN standard.
You should open the User Interface of the scanner and enable "access from local computer" if you want want to work with network scanner from computer to which scanner is connected. Scanner may not support "access from local computer" feature - for more info you should contact scanner's manufacturer.
We also have a network scanner which is connected via IP. One each client machine we have installed the Twain driver that came with the network scanner/photocopier/printer and it works just fine. The TWAIN drivers/software recognise where the scanner is and work to that location. Most of the larger Brother, Minolta, HP and other manufacturers have Client installs for TWAIN scanning.