The standard rule for item creation is that the item creator pays all of the associated XP costs for the item being created. However, this makes it difficult for the party wizard to keep up with the rest of the party when he's spending time and XP creating magical gear for the party.
Sharing XP CostsEdit
An item crafter may extract up to half the base XP needed for creation of an item from another character. That character must be present for the entire process of creating the magical item, and is subject to the same restrictions on his activities as the item crafter.
Artificers and Sharing XPEdit
Artificers have access to the cost reduction feats in the Eberron Campaign Setting. These cost reductions do not modify the base XP needed to create a given item; thus, an artificer who possesses these feats may extract more than half the final XP cost for a given item from another character.