Tony's advice is very good. I do have a couple of points to add.

Something you need to be aware of with the 4x3 vs. 16x9 choice is burn in. CRT's get dimmer as they age. If you are only using a portion of the CRT face then you will get uneven wear and it will become visible. For example, if you have a 16x9 screen but you primarily watch TV in 4x3 mode, the 4x3 square in the middle will become darker and you notice that when you do watch something in 16x9. Some (all?) 16x9 RPTV's use gray bars instead of black to avoid this. Many find these gray bars objectionable. A good solution if you don't mind the hassle is to display the gray bars but physically mask the screen with something like black cardboard fastened with velcro.

Tony is absolutely right about the interaction of heavily compressed digital video (like DSS and DISH) and marginal line doublers. This is made much worse by improper calibration (more below). One option is an external line doubler. You can get a pretty good one for $500 that is likely better than what is in the TV. However, some HDTV's have compatibility issues with external line doublers. The most common problem is that the TV locks in widescreen mode when receiving a 480p signal. (480p is what you'll get from a line doubler or progressive scan DVD player.)

Mostly, you just have to accept how crappy DSS and cable are when blown up to a large size. I have a 100" screen with my front projector and I've gotten used to it.

My final bit of advice is no matter what you buy, get the AVIA DVD and follow it's instructions to properly calibrate the user settings. Nothing you can do will improve your picture more than this.

-Dylan