install application on mac

hi im having several problems with my mac.. which i've already downloaded the installer for skype, stuffit (to compress .zip file in mac), oovoo, etc but once I clicked on the installer and I want to install the application, the application logo has slash on it and I can’t drag it to the application folder. There’s also a message saying that “the application can’t be installed because this program is not supported on this architecture”..
what should I do for this case
Thanks a lot =)