Rika,
I'm using the
GIRA Homeserver to add additional functionality to my EIB installation (visualisation, logfiles, scenes, logic, ...). This is a separate server running a some linux distribution and not having any moving parts (disks, fans or alike). This box is designed to keep running day-in and day-out for several years (as opposed to a normal windows box)
This is also the box that is able to map IP telegrams on to EIB commands. It also has the web-based visualisation. Pretty nifty device imho, downside is that is will set you back a respectable 2000 euro's.
If you just want to be able to send messages on to the eib-bus you could use the
EIB ASCII terminal from Schlaps. This 'gateway' comes with drivers allowing you connect to the EIB bus using Visual Basic or Javascript. It does not have any logic or so on board, just passes your commands. Price is about 500 euros.
If you want to go 'deeper' you could use the
Falcon components. These are a set of DCOM libraries facilitating communication with the EIB bus over the standard rs232 or usb gateways. No idea however on the license fees. This thing is mainly used by third party developpers. (I think that the eHem product you mentioned uses these components)
I believe that there are also some open source like initiative in progress. I'll check to see if I can find any info on those for you
Hope this helps.
kris