So, you have a tar file with absolute paths...now what?

Don't do it again. :-)
After you have already created one, the easiest way to "un-absolute it" is to use GNU tar. This is the default behavior when creating or extracting files with GNU tar.

You can find GNU tar at gnu.org/directory/tar.html.

You are welcome.

Another tip came in from Gregory L. White who suggested using pax:

# tar tvf export_home.tar
tar: blocksize = 3
drwxr-x--- 201/1        0 Sep  5 10:16 2003 /export/home/gwhite/x/

# pax -r -s ',^/,,' -f export_home.tar

# ls
export  export_home.tar