You are doing great work here. Can I do this with the normal IDE to or do I need special tools (I'm on win 7 )
Do you also intend to implement an USB printer?
You should be able to use flip to load the firmware in windows: http://www.atmel.com/dyn/products/tools_card.asp?tool_id=3886
You'll need to put the UNO into DFU mode and then use flip. You can put it into DFU mode just by connecting two wires as seen here: http://arduino.cc/forum/index.php/topic,52447.msg374201.html#msg374201
; hold wire 1 on the pad, touch wire 2 to the left side of the capacitor for a second or so, remove wire 2, remove wire 1 and the UNO will be in DFU mode ready to upload new firmware. Unplug the USB cable and plug it back in and the UNO will appear as a MIDI device. Note that you can't load sketches when the MIDI firmware is loaded, you have to go through the process again and upload Arduino-usbserial.hex before loading you sketch with the Arduino IDE.
Regarding a USB printer driver, I have a feeling that the firmware would be too large for the 4KB of flash space that's available on the atmega8u2. I'm curious as to what you would do with your Arduino if it could be a printer device?