My daughter has the "Corrupt Installer" problem. This morning I checked under FAQ and found this information:

Q: I am trying to install LimeWire on the Mac, and I keep getting an error message saying that the installer is corrupt. What can I do??

A: Increase the preferred size of the installer in the "Get Info" window for the installer file, and then run the installer again. If the installer gives you another error, reboot your computer and run the installer one last time.

In order to increase memory you need to click on the installer icon to highlight it, which activates the Finder. Then look under "File" and scroll down to "Get Info". When the box comes up, click on the drop-down panel that says "General Information" and you have a second item labeled "Memory" where you can change the numbers. An earlier poster suggested increasing it by 1000. I don't know if this will help, but it is worth a try.