p7zip is not in the default image, and there is not a package for it in the Angstrom repos. There appears to be some x86 assembly in there. I tried to get it to compile, but ran into problems and gave up. Admittedly though I only gave it like an hour or so of effort before I just opened the .7z on my desktop and zapped the contents over to my Pandora. Someone else might have more luck.