its microsoft. if they wanted to they could make leprechauns fit on a cd. heck if they wanted to they could make a leprechaun dance on a cd.
what i think they do is compress it with a program (i use to know the name of it), that can compress a file more then conventional compressors. then they use a special kind of compressor to compress that, i think. thats the only way i can think of for them to get it so long. the compressor is probably something similar yet better then winrar, which is a much better compressor then winzip. actually it maybe more similar to the mikki super compressor, which is the best compressor that i know of.