Read this first:
Then get this:
Feeding a 1080i HDMI signal is the best thing you can do for the PRO 900, it's too low an end of set to really benefit from the money you'd spend on a scaler.
Do you have the large setup remote, and do you know how to converge, because the PRO 900 is a pain to set up if you've never done it before.
I have one setup remote left if you need one, and if the tubes are in decent shape (check that before you spend anything on this set), it will throw a nice picture.
If you've had this since new with video only sent to the projector, then you've been stuck in 1st gear in a 5 speed. You'll love the upgrade HD will give you.