I have followed the instructions on this eHow page but I couldn't get them to work: How to Flash a Custom ROM on Samsung Galaxy S

When I reboot into recovery and install .zip file from my SD card I get an error message.

I am interested in getting the Darky Rom OR if anyone recommends a better rom which runs faster I would be happy to go with that. I am not sure what kernal to use because I don't really know what that is. =S

Also, I would prefer not having to use ODIN because I am running on a Mac OS X and I think there is only a Windows version (?). I was hoping there would be a simpler way to do it.

Oh, and my phone is already rooted, so I don't need to know how to do that.

I am really sick of lag and if anyone who is able to provide some clear concise instructions will get many thanks and rep!!! =D