Need answer to Rooting Issue

[park]

Ok, here's whats going on. I've spent the better part of two days trying to figure this out. I rooted my Samsung Galaxy S a couple days ago (using a mac, btw) and downloaded FCM to start using ROMs. Problem is, I cant boot in recovery using Update.zip~ the file refuses to verify. This has me at a junction where I can either unroot or figure out the problem and continue forward. I'd much prefer the latter to the former.
~ why am I constantly getting this error? I've tried several times, and I can't even do an image recovery/backup. It seems as though whatever file is on my sd card is unreadable, or the card itself~ although unlikely, because everything else is operating fine. Because I'm operating off of a mac, I can't use ODIN. is there comparable software for OSX, or is there a way I can use Terminal to push it through like I did when I was rooting? Any advice would be appreciated, this is frustrating me beyond belief, and I know there is someone out there who has done this on a mac.