Here's the offical wording from the "Terms of Use" page:
Quote:
4. Do not create any new Neopets or accounts if you are not going to take care of them. You cannot have multiple accounts just to get more Neopoints or items. You are only allowed a maximum of five (5) accounts and can earn Neopoints with only one (1) account. Users who break this rule can have all of their accounts frozen.
Do not use your other accounts to attempt to gain an unfair advantage over other users by restocking, gaining trophies, etc.
So I would take this to mean that you cannot play games that send points to the high score tables including the referral system; cannot try to take advantage of a restock by having 2 accounts in the shops at once; using you alt accounts to boast the auction price of your own auctions; gain more np from the Advent Calandar, Snowager, Tombola, Grumpy Old King, Coltzan's Shrine, Scratchcard Kiosks, any of the Wheels, and Buried Treasure. I would think that Sponsor games, the Omelette, Giant Jelly, and things like Kacheek seek, Guess the card or Faerie Crossword would be okay so long as you didn't transfer all of the NP earned from the alts to your main accounts.
With transferring items and NP to an alt account - if you can only earn NP from 1 account a day then it would mean in order to maintain and start a gallery account, you would HAVE to send NP and items to your alt account(s) from your main account in order to actually do it without using any of the regular methods to do so.