Create a portable Mac OS X install on a USB flash drive
No, we don’t mean portable as in a laptop, but portable as in a USB flash drive. Here are articles on how to have a fully functional portable Mac OS X installation, one that gained a lot of attention several months ago, and one that has recently topped the Digg charts. Both will direct you step by step on how to get Mac OS X booting live from a USB pendrive to install. Supposedly, using the same procedure, you can even boot Mac OS X from an iPod! For best performance be sure to use the significantly faster USB 2.0.
Install Mac OS X from an external firewire hard drive or USB flash drive
OSx86 ONLY: Boot Mac OS X x86 from a USB Pendrive – this is for OSx86 (Hackintosh)
Update: we will soon have our a tutorial to do this that will be modernized, stay tuned! In the meantime, you can follow the instructions on installing Mac OS X from an external hard drive and they are virtually the same.