I downloaded the iso but can't figure out to make it boot from a USB flash drive.
First you need to burn the ISO to a CD, then using the installer (one of the icons on the desktop of Puppy when you run the CD) you set it up in the USB. Check the Puppy site, there are instructions for this in details.
Robert Collard, Springfield, IL
Dell Inspiron 1545 Laptop, Intel Duo T3400 CPUs @2.16 Ghz. 4GB RAM
Linux Mint Debian Edition, Xfce 4.6.2 Desktop, 2.6.37-0.dmz.6-liquorix-amd64