does anyone know if sounbooth cs4 is completely compatible with ppro cs3

Do you mean to ask if you would lose your show if you installed CS4 over CS3? I'm not sure, but I am having CS4 installed over CS3 in two weeks. I'll let you know.

I mean...I have absolutely no intention of upgrading ppro cs3 to ppro cs4 but I am looking into soundbooth cs4. Will soundbooth cs4 work well with ppro cs3

I can't speak to Soundbooth, specifically, but I know of, and have had problems with, different Adobe products conflicting when CS3 and CS4 versions are installed. The primary problem I've encountered has been with licensing. Apparently, there are common files used by both CS3 and CS4 programs that administer the licenses. I've always been able to straighten things out, but it has almost always taken a call to Adobe to do it. I would think the problem would be aggravated if suite versions are involved.