5.0.x.x is a pretty old version - if your registration covers you for 5.5 (and AFAIK, a 5.0 one does, unless you were already on an upgrade to 5.0 from a 4.0) - that should have far more supported drives.
Do you mean WinXP Pro? - pretty sure Nero 5.0 is way too old to support XP ... came in at about 22.214.171.124 if I recall? http://www.nero.com/en/631933457317970.html
Previous version updates are here...
I belive the 5.5 is actually an installable - the 126.96.36.199 is a small update only, though Nero50.exe (install) is also on the FTP.
With 5.5, all the versions tended to be DEMO / Registerable / Update in one.
PS. CCampbell is the expert on Nero
Mind you, it sounds like it's more than a Nero problem, if none of them work, unless that old version of Nero has screwed it up!