Are you planning on watching "protected" (read: artificially crippled) HD content (HD-DVD/Bluray) on Vista or through a stand-alone player? If not, then I kind of doubt there will be any improvements over the 2005 other than the HDCP (with the possible exception of Component input). I also think the 2007 is going to be pretty expensive at release, at least compared to what you can get a 2005 for these days. I have a hard time recommending the 2005 if HDCP is going to be important to you, but at the price premium it's almost certain to come with, I don't know if I can recommend the 2007 for sure either...
Edit: For what it's worth, there are apparently ways to get around HDCP already - but the devices that can do it will cost you enough money that buying the 2007 over the 2005 would be cheaper.