This is an extremely neat, well thought out box that will accept an Arduino Duemilanove, Diecimila, NG or an Arduino Mega. There is enough room to fit an Ethernet shield onto your chosen Arduino. Open cutouts already exist for the Arduino power + USB jacks. Sliding panels are provided to give access to the shield's LAN socket should you fit it.
Inside - 4 posts fit through the boards' mounting holes - forming a secure mounting. No screws are required, but you may wish to use a little glue if you only have one board in the case.
Depending on the board you're using, there's also room for a 9V battery!
This is a lovely box - perfect for encapsulating in a neat, presentable package, a wide range of Arduino projects. It's not a 'one size fits all' box - but you can do a lot with it.
A few notes - the ABS plastic is flame retardant, opaque + black. Also the case does not come suppied with any of the boards or the battery shown in the photo. Just in case you're in any doubt, no part of the box is transparent. Dimensions are 104x54x30mm