"Solitaire Greatest Hits" and "Alfred" "Can't be installed on this computer" although I've been successful with several others. When the iTunes app store was newer I kept coming across apps that couldn't be installed on my iPod Touch for no apparent reason. Turned out the developers had to check boxes for devices their apps could be installed on. Some hadn't tested theirs on the Touch, some didn't care, and some just missed the box for the Touch.
I had this problem after a completely clean install of Mac OS X 10.6. Repairing permissions, deleting the App Store, reinstalling the combo updater, and other solutions suggested in this thread and others did not help at all.