It would be interesting to extrapolate the 2000-2004 Bush/Kerry vote trends to figure out which states will be red and which states blue in '08.
The matchup makes a huge difference.. I don't think you can project for 2008 based on 00 and 04.
For example, Kerry beat Bush by over a million votes in NY, so closing the gap by another 300 thousand wouldn't flip NY from blue to red in '08.
On the other hand, Kerry beat Bush by less than 200 thousand in Michigan, so another 567 thousand net Republican votes puts Michigan in the red column in '08. A similar analysis shows NJ going from blue to red in '08.