Which Arduino?

There are several Arduino "clones". They are all compatible and have different enhancements and optimizations. For example some have smaller form factor, others use the surface mount version of the chip; some are a little cheaper, some have more powerful versions of the chip, some are available as a kit, etc.

For the HIFIDUINO, I believe the basic Arduino will do. My favorite Arduino clone is the Seeduino from Seeedstudio.com. You can purchase it in the us from NKCelectronics. The current version of the board is 1.1 but there is an update being developed with the more powerful version of the micro controller chip. You can follow the development of Seeduino in the Arduino Forum.

Why is this my favorite? Well, I like surface mount technology, I like the mini-usb connector and it has the pin-outs aligned to the grid of a bread-board. You can download the manual for Seeduino here. You should also read the reference to the Arduino board from which it is derived.

Here is a photo of Seeduino 2.1 prototype.