For my project I did not require more than the ports available but was short a mouse and used one from another box to get set up..when I went to get one, I got the usb with adapter as it would have the best recycleability and it works fine with the included adapter
I'm using a USB mouse with PS/2 adapter on my Celeron desktop. It's actually part of a Logitech wireless keyboard and mouse set and it came with PS/2 adapters for both the keyboard and mouse wires from the wireless transmitter. (For those not familiar with these, the mouse and keyboard are wireless but the transmitter plugs into a USB port. It comes with PS/2 adapters for those who prefer or have to use PS/2.) I have two USB 1.1 ports and three USB2 ports on that computer, but I didn't want to use the USB ports for a mouse and keyboard, given that I had PS/2 ports.
USB mice that come with PS/2 adapters do work fine, but attaching an adapter to any old USB mouse will very often not work.