Please download the .dmg file from other resource or download it from other machine. Try to use that, it should work. I also faced the same issue and I went through using different installer.
I have the same problem, but I am already on OSX 10.7.5.
Any ideas? I have no InDesign (CS5.5) at present, and cannot work!
I had some errors on In Design, so I though I would uninstall and reinstall. Bad idea.......
Some further background info. I first of all just reinstalled InDesign. But that did not help, and it was on a go-slow, so I thought I would do a complete uninstall-reinstall. So immediately before this problem I had already done an InDesign install without any problem. It was only after I did the uninstal, that the problem started. I tried a 'clean' as the manual suggested, but there was nothing to clean.
I will try redownloading the CS5.5 installation file again. But since it takes 3 hours to down load, I shall go to bed and try to install it in the morning.
Same problem here with InDesign CS5.5. Then after downloading it from adobe I get the same dialog box "Install" can't be opened. You should eject the disk image. Which turns out to be a vicious cycle.