keyboard wireless or usb??

If the Bluetooth wireless keyboard you want to buy has got an external Bluetooth receiver, buy an USB keyboard. Only some Bluetooth wireless keyboards are detected when your computer is starting, and if OS X fails to start, you need to press some keys to solve this, so you should buy a USB one. A Mac detects a Bluetooth keyboard just when you press the start button

Any KB other than Apple's, but USB is the only way to go really.

If a PC KB, usually Windows key = Mac's CMD key, alt = Mac's Option/altkey, though some are reversed.

I've been using this > Desktop MK120 mouse and keyboard combo with my Mac Mini for over a year now. You can also get just the Keyboard K120 on sale at most Electronics and Office outlets.

even a cheap one like this will work...

http://www.directron.com/kt400u2.html

Any will work, note that the location of Windows, ctrl and alt keys may be puzzling to you: win key is Apple key, and ctrl and alt have a different location as compared to Win [= Apple, i.e. command] key.

If you decided for a non-Apple keyboard (I would try a sh keyboard first), you may perhaps change the location of some initial keys in Sys pregs/keyboard/modifier keys and also to try a 3rd party utility like DoubleCommand or KeyRemap4MacBook.pkg (useful for any keyboard, not for MacBooks only).

As a user of various keyboards, just one more word: Apple offers the best and comfortable keyboards, you will notice the difference immediately. If you could afford a mac, perhaps you can afford at least a sh Apple keyboard. Give a try to this first.

to be clear: you may use ANY usb keyboard; some bluetooth non-Apple models may be problematic with commands upon boot (after chime), but any USB keyboard will do its job.