I made a quick video showing how to use a usb keyboard with your Acer Iconia A500 Tablet.
If you have any questions please let me know.
Now that Acer has sent out the update to Honeycomb 3.1 you can also pair and use a bluetooth keyboard. Here's a link to a video how to for that as well. http://www.youtube.com/watch?v=EcxahxHJrZg