you could also have the arduino emulate a ps2 mouse. and either connect directly to the ps2 port on your computer or use a ps2/usb adaptor (these are typically $5-10 and do both keyboard and mouse, the small ones that come with your mouse are typcally only a plug converter). This pay you just plug it in and go. I would suggest using the adaptor so that you don't run the risk of damaging the ps2 port. BTW the ps2 library in the playground only implements the host side of the protocol and not the device side.