Downgrading Kernel on Live USB

[hightech]

How would I use the 2.6.38 kernel? I understand I can make the changes in grub.conf, but im using a live usb.

[iproute]

you'd probably need to compile it, which certainly can be done, but you'll probably not get much in the way of help here.
Should be something close to this
http://berm0o0da.wordpress.com/2011/...0-04-from-ppa/
Looks fairly similar to what I do with gentoo kernel compilation. I've never done an ubuntu kernel, but it's likely that the backtrack .config or config.gz is somewhere in the filesystem.

[iproute]

BTW, my reference was not meant to be a step by step guide, so it'll take some creative work to accomplish kernel compilation. If you've never done it before(compiled a kernel), check out the gentoo handbook, which granted is distro specific as far as getting the source goes, but is fairly generic otherwise.
http://www.gentoo.org/doc/en/handbook/handbook-x86.xml