Multi-Byte Operations

I am just starting out learning assembly. I know it is a heck of a lot easier to write code in C but I will have to learn assembly for a future university class so I figure I might as well start now and get a jump on the class. I was wondering if there are any good tutorials on multibyte atrithmetic and other multibyte opperations. Pretty much, I need some tutorials with working with multibyte numbers.

Any help would be appreciated.

Here's some stuff to chew on. (chew = multi-bite) :)
http://www.piclist.com/techref/microchip/math/index.htm

thanks a lot, lots of useful info for me.