First off, I am not one of the Peercoin devs, but I am a big fan of the coin and the dev team. I saw a post recently about adding a Mac client but I do not think this has occurred yet (I too do most of my recreational computing on a Mac). Maxpower is the handle of a community member here who has created many Mac clients where necessary - if you want a more immediate solution, send him a PM and I am sure he would be happy to assist (just throw him some coin as a donation for his effort). Regarding the checkpoint warning, this will show until the whole block chain downloads. Just make sure you have the most recent version and if the block chain downloading seems to get stuck, close the client and then reopen it - this helped me when my download seemed to slow or get stuck. Hope this helps.