It is easy to take a Xastir live CD image and install it on a usb drive.
First download unetbootin at http://unetbootin.sourceforge.net/
Then download a Xastir Live CD iso image - they can be found at Downloads under Bootable CD's.
As of this writing, I have only used the windows version of unetbootin, so the following applies to it. There is documentation on how to use both versions at the url above.
1) Launch unetbootin, and select Diskimage in the left center of the window.
2) Leave the Custom option deselected.
3) Browse to the location of your Xastir live CD iso image and select it.
4) Select the correct drive letter for the usb drive you are writing to.
5) Click OK
The result is a bootable usb drive that will boot your favorite live CD.