It would help to know a little more about your problem
If you have installed a new operating system, and want the old one back: You would need a recovery disk of the old operating system.
If you want to revert the operating system back to its factory settings: You can use a recovery disk. Some operating systems have a function that allows you to restore it to a previous state.
If you do use a recovery disk, make sure you back up all your data (save all your pictures, word documents, files of importance) in some sort of external media (external hard drive, or flash drive).
Yes. There are laptops with Android OS .
No, Some of the laptops come with their own OS like Macintosh(Mac) OS used in all Apple's laptop. Rest all the laptops can run with Windows XP regardless of the hardware used.
Disconnect from the internet.
No. It can be used on any Mac OS X or Windows computer.
Mac OS X is the operating system for all of Apple's current Macintosh computers including iMacs, MacBook laptops, and the Pro models. The current version of Mac OS X is 10.6 (Snow Leopard) which can be updated to the latest revision10.6.2.
Mini Laptops have been released by many companies. Mini Laptops are being made by Sony, Dell , Apple and HP. But they are costlier than normal laptops.
Ubuntu can be installed on a Mac or run from a LiveCD (See links below). It can be run on a virtual machine on top of Mac OS X.
No a RTOS is used only for real time applications and does not have many needed feature of a normal OS.
Legally Mac OS X can only be installed on computers made by Apple. Some people have had success installing it on other computers.
Quickplay can be download fron website and from CD it is for all type of OS and for laptops.
Leadership reverted to the emperor <------- novanet answer
The only computers supported running Mac OS are Apple label computers. They also deliver the best performance.