"All your base belong to us!" is a quote from the poorly translated English introduction to Zero Wing, a side-scrolling video game by Toaplan, released in 1991.  I can't explain it much better than a Zero Wing faq:

"All your base are belong to us" is the Zero Wing fad.
It stems from The Laziest Men On Mars song, "The Invasion 
of the Gabber Robots" merged with a Flash animation that 
BAD_CRC did.

I downloaded a copy of the .swf file.  If anyone wants it e-mailed to them just drop me a line in my e-mail and I'll return it in reply.