linux
Creating a CentOS USB drive on Mac OS X
Download .iso, either netinstall or LiveCD.
get mounted disk by inserting drive and running diskutil list
unmont disk by running diskutil umountDisk /dev/disk3
write image by running: dd if=~/Downloads/centos\ 5.4/CentOS-5.4-x86_64-netinstall.iso of=/dev/disk3 bs=1m
run diskutil eject /dev/disk3
try it!