Eureka with me with 1 card, my opponent with 4

[LotusHead]

Eureka: 2GG Sorcery
Oracle text: Starting with you, each player may put a permanent card from his or her hand into play. Repeat this process until no one puts a card into play.

So my opponent had this nice Magus of the Vinyard deck with Eureka, and gets it off turn 2 or 3.

I had a pretty nice hand for Stax (1st turn Juggernaut), but..

He played Eureka, and put something into play (It might have been Nichol Bolas, Planeswalker)

I had 1 Crucible in hand (and 1 in play already), so I was ready to end this BS. (I thought he played Legend Nicol Bolas with no upkeep resourses availiable.)

I said : Done.

He then dropped a few more permanents (most relevent: Platinum Angel).

I thought that Eureka worked like so: Caster drops a permanent, and I drop a permenent. Or I don't, end spell.

He thought it was "Players drop stuff (both of us) until one of us doesn't. (clearly, he had lots to drop...).

How does Eureka work?

He later said that when I attacked with my Juggernaut, I would have to declare what it was attacking (ie, HIM or his planeswalker.) I'm pretty sure that he would have to declare (or not) blockers, let my combat damage go onto stack, and THEN I decide whether or not to do damage to him or plansewalker).

[IthilanorStPete]

Your opponent was correct on Eureka. To quote one of the rulings:
"Each player gets a chance to put a card in play starting with you and going around the table to the left (unless your multiplayer variant defines a different ordering). A player may decline to put a card into play when it is their turn. The spell ends when all players decline in a row. [D'Angelo 2002/01/10]"

And yes, you have to declare whether you're attacking your opponent or the 'walker when you declare attackers. It doesn't work like noncombat damage; if you Bolt your opponent, you don't choose whether to redirect it to the 'walker until it's resolving.

[wiley]

_PLANESWALKERS IN COMBAT_
Planeswalkers aren't creatures, so they can't attack or block. However, planeswalkers can be attacked.

As the declare attackers step begins, if the defending player controls a planeswalker, the active player declares who or what each attacking creature is attacking: the defending player or one of that player's planeswalkers. All the attacking creatures may attack the same thing, or they may attack different things. If the defending player controls multiple planeswalkers, any or all of them can be attacked during the same combat phase.

As the declare blockers step begins, the defending player declares which creatures he or she controls (if any) are blocking the attacking creatures. The blocking creatures don't care who or what the attackers are attacking.

During the combat damage step, damage from unblocked creatures attacking the defending player, damage from blocked creatures, and damage from blocking creatures is assigned and dealt as normal. Unblocked creatures that are attacking a planeswalker assign and deal their combat damage to that planeswalker, which causes that many loyalty counters to be removed from it. Planeswalkers, like players, don't deal combat damage.

Taken from here: http://forums.gleemax.com/showthread.php?t=933352

[Anusien]

Eureka {2GG} |Sorcery| Starting with you, each player may put a permanent card from his or her hand into play. Repeat this process until no one puts a card into play.

It's sort of like passing priority; the effect won't end until every player chooses not to put a permanent card into play.  So if you say "Nothing" and he puts a Platinum Angel into play, you still have a chance to put something else into play.  Every player has to not put a permanent into play in a row in order for the effect to end.
IthilanorStPete has it correct here, but that ruling is 7 years out of date and things may have changed so I wanted to chime in with an up-to-date explanation.

And yes, Planeswalkers can be attacked and blocked like players.  Wiley has the relevant rules.

[LotusHead]

Gosh. I wholeheartedly appologize to whoever it was I was playing against.

He did have a neat deck. Thanks for all the responses/explanations!