Are there any non-Apple multi-touch trackpads on the market?
Yes. Bamboo tablets made by Wacom are an option: they allow multi-touch and stylus input on a pretty large surface, but are more expensive than a magic trackpad: the cheapest I believe costs $75 USD. Wacom is a company that builds touch devices for graphic designers and consumers. Perhaps you want to give a look to their website:

http://www.wacom.com/en/Products/Bamboo/BambooTablets.aspx

In case though, you want to use the Magic Trackpad, Windows drivers for Apple devices are downloadable in the form of Bootcamp Updates from the Apple Support page. Alhtough the trackpad is supposed to be Mac-only, after a bit of googleing I found a couple tutorials explaining how to use it with Windows. 

Here is a blogpost I found, and a webpage with instructions:

http://www.mannis-world.de/blog/?p=15

http://www.labnol.org/software/apple-magic-trackpad-with-windows/14158/

About using multitouch with any other laptop: I don't think this is possible, for it requires hardware features not present on most laptops. 

Hope it helps!