So, if I got PS3, I'd need to get soemthing like the HM-31. Using a DVI/HDMI cable, I'd hook the OPPO 971H to the HM-31. I'd use an HDMI cable to hook up the PS3 to the HM-31. Then I'd use a 2nd DVI/HDMI cable to connect the HM-31 to the TV. That, in turn, would get me 1080i video.
You've got it, all the way through. HDMI/DVI from the 971H to the switch, HDMI fron the PS3 to the switch, HDMI/DVI from the switch to the TV, and you're all set.
Is the difference between 1080i and 1080p significant?
It depends on a lot of factors. Screen size, viewing distance, display type, and even source material will all be significant factors. Personally, I wouldn't pursue a display upgrade solely to have 1080p. If there were other reasons to make an upgrade, that'd be one thing, but just for the sake of the "p" alone I'm not sure it's going to be a great deal. Remember, also, that the 971H's maximum output resolution is 1080i. OPPO didn't start supporting 1080p until the 981HD.
Any recommendations on a 1080p TV in the $1500 range?
Others are probably better informed on the current TV offerings, but screen size range will certainly be necessary to help with that. My initial guess is that your current CRT would be hard to beat in its size range even though it can't do 1080p, and a larger display that offered 1080p with better performance than the CRT would likely land outside that $1500 price range. I could be wrong, though - like I said, I haven't been keeping a real close eye on the current offerings.