The Mac uses the exact same USB connectors as any PC. Just pick the multi-button USB mouse of your choice, and the keyboard of your choice, and plug them in. You will probably need a driver for the extra buttons of the mouse (read on).
You're better off selecting your _own_ 3rd-party mouse and keyboard, anyway. Since the company moved to USB (replacing the old Apple mouse/keyboard connection architecture that was called "ADB"), they have yet to offer either a keyboard _or_ a mouse that is [in my opinion] usable.
For a keyboard, I would highly recommend something by MacAlly called the "iceKey". It has a traditional "feel", is full-sized, and has a couple of rows of programmable buttons above the normal keys, which you can set up however you like. These sell for about $28 or so. Try "macally.com".
As to the mouse, I found the relatively basic Microsoft "blue" mouse to work just fine on my PowerMac g4 1.25ghz dual-processor desktop. To drive it, I use something called "USB Overdrive", a shareware utility that is customizable to _any_ mouse you plug in - really good software. I believe you can find it at "usboverdrive.com".
If you're seriously considering a Mac Mini, I'd suggest spending the extra $100 for the faster CPU and larger hard drive. At this point, it's unknown whether the internal CPU will be upgradeable in the future.
- John
The iceKey slim keyboard is definitely the best.
The only reason I was considering it is because I've been looking for a way to get my 70 year old mother to use email and Internet access. A WinPC is out of the question. An Apple would be good because of the stability and ease of use...but the price always was the stumbling block. If this new mini-Mac is stable and easy to use for a woman who is a techno-dunce, then it might be worth a shot. I have plenty of peripherals on hand to use to complete the package.