The Sheevaplug is the previous version of the GuruPlug. The only differenct is that it has fewer interfaces. There is only one network interface, one USB interface but it has the JTAG-board included in the plug.

Links:

Take a look at the official GlobalScale website for detailed information

Here are instructions on how to install Debian on the Sheevaplug. Haven't tested it since I dont have a Sheevaplug.

Here is a tutorial for Debian Lenny and EIB/KNX, haven't tested it either