Are you the DM? If so, that simplifies things. :)

I don't understand your first question. I know of no rule that says an attack does a minimum of one point. There is a rule that if damage reduction negates all damage that special effects of the attack do not take place, but sneak attack is part of the damage, and not a special effect.

SR: DMG, page 299, "Check spell resistance only once for any particular casting of a spell or use of a spell-like ability"

SR: Thanks for that, I don't have access to the DMG. Everyone else was right, I was wrong.

Damage: Leather PHB page 135 "If penalties reduce the damage result to less than 1, a hit still deals 1 point of damage". Not quite what I said (damage reduction's not a penalty).

The situation I was was in that I did not know whether creature I was attacking was undead or not. I have a STR of 9 (hence a penalty of 1), a normal rapier and +4d6 sneak attack. I rolled a 1 for my die roll and 10 more for my SA. I claimed this meant that if this was a valid sneak attack, I did 10 damage.
1-1+10=10
The DM said I did 11.
(1-1=1 using that rule)+10=11

I imagine that had I not had to nominate the rapier die for this particular reason, I would have continued to get away with just rolling 5d6-1 and saying the total, and am pretty sure I'd be correct in doing so: I think I just flummoxed the DM on this occasion by having ten pips of dice on table associated with sneak attack and announcing that the difference between the sneak and non-sneak damages was nine!

I've convinced myself some more but am I right?

As far as I care, yes, you're right.

The "minimum damage" rule is for the attack as a whole, not just the weapon portion of the attack. A three-strength rogue should do less damage than a nine-strength rogue given the same die rolls.

Ah. The penalties from strengh apply to the damage die only. It it goes below 1, then it stays one. 1d6 with a -4 for str is 1d6-4, with sneak attack would be (1d6-4)+1d6. I don't know that this is in the rules, however, so you might have to consult the FAQ or ask Skip.

That's the way I think it works and we've played it.

SR: Thanks for that, I don't have access to the DMG.

System Reference Document:

http://www.wizards.com/default.asp?x=d20/article/srd35