http://seer.support.veritas.com/docs/252928.htm provides info toupgrade from v7 to v9, but involves installing v8 as an interim step
v7 will not run on W2K or W2K3, so you would have to upgrade NT to v8, then upgrade your OS, then upgrade to v10 (I assume that this should work, since it uses the same underpinninga as v9 - MSDE/SQL etc)
You would probably be better off just installing v10 on W2K3 and building out all your media sets, job defs etc from scratch.
You should still be able to import all your v7 catalogs, tho. Do a special backup of the \Catalogs directory before you start. then once v10 is installed, shut it down, inventory and catalog the tape with the \catalogs dir on it, restore all the U01 files to the new \Catalogs directory and see http://seer.support.veritas.com/docs/231585.htm to force backupExec to re-inded the catalog.
