Congrats on the purchase, but the keyboard problem seems odd. I've used wired USB keyboards with my A500 and no problem.
I've even used a logitech wireless USB keyboard and mouse kit with no problems. The A500 even came up with a cursor for the mouse and the keyboard music button even started the music app.
Is it possible that one of the keys, eg ctrl or shift, is stuck on your keyboard? Does it work OK on a PC?