HDR is awesome, I don't know how anyone who is capable of running it chooses not to, without it the world looks flat and lifeless to me. Maybe it looks better on the ATI, it seems to be mostly nVidia people who turn it off.
Even if it does look just as good on nVidia, you might not be happy with the performance on a 7600GT - I've got an x1900xt and I rarely see more than 40fps outdoors with HDR and everything cranked up.
Maybe performance is better with the new patch and drivers, I wouldn't know, I stopped playing because I was sick of buildings, trees, and huge boulders suddenly appearing 10 feet in front of me.