> If I want to rip a DVD to my hdd, I use ImgBurn?
No. ImgBurn as its name suggests is an image burning application. It is not a ripper.
> If I want to copy a DVD (and compress it in the process), I use ImgBurn
No. It isn't a compressor either.
> If I want to burn a DVD from IFOs/BUPs on my hdd, I use ImgTool and ImgBurn?
Yes, if you wish to and assuming that you also have the relevant vobs.
> and I no longer need DVD Shrink?
Well you will unless you use a different compressor.