None of the WiiBrew media apps will read my external USB drives. I think it's because the drives were formatted on my mac. I had a drive that was formatted on a dell and, more or less, worked perfectly with mPlayer CE. Then I got an Apple laptop, reformatted the drive (myPassport) and....nada. Suggestions?

Was it formatted as HFS+ (Mac OS Extended, I believe) or Unix File System? If so, most homebrew does not support it, including the Homebrew Channel itself. If you formatted it as something else, there should be no issue.

Don't forget that the partition map should be MBR instead of GUID.