nhl.com mention

nhl.com has a preview (or, short little blurbs) of the various leagues...what they start with for the ECAC:
Remember a pipe-dweller from Cornell named Dryden?
"David LeNeveu has a chance to be one of the best goalies we ever had here," said Big Red coach Mike Schafer. "And those are pretty strong words, considering the number of goalies this place has produced."
Put Hobey finalist Doug Murray, a defenseman, in front of LeNeveu and you get two of the key contributors returning from a squad that led the nation in team defense. Add imposing forward Steven Bâby, and all the parts are in place for a possible parade in Ithaca come April.

And at the bottom of that article:

"The Frozen Four for 2003? Boston University, Cornell, Denver and Michigan.

The national champion? Denver."

one representative from each of the big 4 conferences? how many times did that happen in the past?

Four times:

1996: Michigan, Colorado College, Vermont, BU.
1994: Lake Superior, BU, Harvard, Minnesota.
1989: Harvard, Minnesota, Michigan State, Maine.
1988: Lake Superior, St. Lawrence, Maine, Minnesota.