Wireless keyboard/mice: software, EULA and plug n play?

I have recently looked at some wireless keyboards. Some that are microsoft
keyboards mention there is software included.

Most sales people I talked to said wireless keyboards and mice are plug n
play. I pretty much only need drivers for an operating system.

Some wireless keyboards and mice say they work with XP and Vista, but don't
mention windows 7. Others mention windows 7. Can I use all wireless
keyboards and mice? Can I get the right drivers or are there actually
limitations to the hardware with each OS?

Since there is software to install I am concerned about not being able to
use certain wireless items on other systems I own. Most notable are the
microsoft products, since I have an EULA for windows XP, I am concerned about
that kind of stuff. Does anyone know about the software usually associated
with the wireless keyboards and mice?

I have a desktop and laptop, I need to be able to plug a keyboard and mouse
into my laptop occasionally and then connect the laptop to my monitor. Can I
do this? Or use the wireless hardware on a new computer I could buy in future?