Is there anyway to boot from a flash drive on mac. Can I put a program on a cd to tell the mac to boot from the flash drive.
Start up mac with cd in the drive and flash drive in the usb port. hold down the "C" key as the mac starts up. the mac then would try to boot from the cd. the program on the cd would then direct the mac to the flash drive. on the flash drive would be an operating system installer, like ubuntu or mac os x 10.5. the mac would then install the operating system like normal, except it would do it from the flash drive.
The link provide by hawks does provide all the basics of booting on mac, so you might want to read it carefully.
You don't need a CD to boot from another device. Just hold Option at boot, and all available options will show, including install CDs or OS on external hard drive. Just select the one you wish to boot from.
The reason I suggested somehow using a program on a cd to redirect the mac to boot from the flash drive is because, my particular Mac absolutely refuses to boot from the flash drive (what I mean by this is that when the flash drive is inserted into the mac and I boot the Mac while holding down the option key, it does not even give me the option to boot from the flash drive).
I prefer Macsales over Newegg. Newegg does not specify a lot of information needed when you need to order a product and when I called customer support the people there had no idea how to help me because my product was a Mac. I called Macsales and they even walked me through the installation of a harddrive once, they're awesome, their products cost average $10 more, but is SO worth it when you need their help!
As kbits says, PowerPC Macs won't boot from USB disks but will boot from firewire devices. (That's certainly true of my Mac Mini.) So I would certainly assume that they couldn't boot of a USB flash drive.