AE 7 is actually now 1.5. And actually actually it's now 2.0 - Adobe just released a new version bundled within its Video suite.
6.5 is still a mighty fine program. 1.5 looks nice and has a couple of sweet features, but in all honesty 6.5 is more than sufficient for most users. I'm not sure if 6.5 offers support for HD though and Pro 1.5 does (with optional, free plugin).
Are you upgrading, or are you buying your first version of AE?
I'm perfectly happy with 6.5, and won't upgrade right now. But then, I can't imagine trying to get by without AE.
So, if it's an upgrade, I'd skip it. If you're new to AE, buy it immediately. It will take you years (literally) to master all of the complexities-- hell, I've been working with it for 2.5 years & am STILL learning many better ways to do things with the Total Training DVDs. But you'll be better for it & wonder how you got along without it. It's my Swiss Army Knife.