Willie --How much room do you need on a USB drive for the Acronis Boot Image?
Does it have to be the ONLY thing on the USB drive?
As Cowboy indicated above, a bootable WinPE USB takes only about 325 MB. I made one on a 500MB stick, but the device itself was slow, so I abandoned it. I have one now on an 8GB drive, plus about 25 apps and utilities (AntiVirus, file manager, etc.) that are handy in an "emergency" situation. The whole package uses only about 1.5 GB. I could have used a smaller device, but didn't have anything else smaller.
There is an excellent collection of portable apps and utilities at PortableApps.com, plus a PortableApps environment to manage them all. It's all free stuff -- no "Try and Buy," just free. If you're planning to build a rescue drive, I definitely recommend a visit to PortableApps.