Compare that to the opening night of the Dem convention, when 4,789,000 million watched on cable, and the GOP seems to have the major edge. Remember, though, that Monday's DNC cable number was depressed due to the simulcast of the 10-11pm hour on the broadcast networks.
On Tuesday night of the DNC, however, without broadcast coverage, the cable networks pulled 6,106,000 viewers. One would expect, I think, that McCain and Gulliani would outdraw the relative unknown, Obama, and the not-too-charismatic THK... but hey, the numbers don't lie, right? Advantage: Dems.
Sources:
Drudge has Monday's ratings up on the main page right now (drudgereport.com)
DNC numbers from: http://www.drudgereportarchives.com/data/2004/07/29/20040729_223202_flash.htm