You didn't mention the model of your scanner. It would have been easy that way.
Anyway, the following website tells about the technologies used in sharing a scanner over network.
http://ben.franske.com/blogs/bensbits.php/2005/03/
http://www.edn.com/article/CA420629.html
Since you have mentioned that ur scanner is TWAIN enabled, take a look at the following site that has a list of software that can share it across network
http://www.personalinformationorganizer.com/download/twain/
In recent scanners and MFPs from HP (network enabled), it comes with software drivers to share it across network. Just install that software and point it to the network device. There are also options like "Scan to PC" from the scanner interface itself that will scan and send it to the PC's shared directory.
There are also options in recent HP all in one devices that can share documents through what they call as HP instant share that can mail the images directly, can scan to USB drive etc etc.