i want to run linux on my desktop off an external 500gb drive. it would be going via usb as my comp is 3 years old and doesn't have an esata port. this will pretty much be my first time with linux and i was wondering if i would have any problems running an os from an external drive through the usb. would it be too slow? could i run full programs from the drive on top of linux?

If you want to try Linux, your best bet is to run it from a virtual machine. This is easier to do than to dual boot two operating systems.

Install Virtual PC 2007, then install your Linux distro of choice in that...