• They fed them through Greece, providing subsidized markets and similar. Although you could argue that this was purely self interested since they saw the example of what they had done to Hungary (raping and pillaging). They also kept their cool in the face of crusader provocation, like stealing the lead off church roofs and selling it back to the populace.

• They ferried the crusaders across the Bosphorus, mostly to get rid of them and provided the People's crusaders with guides, which they dismissed -- leading to them being slaughtered almost to a man.

• They transported ships to the lake outside Nicaea to ensure that the siege of the city remained tight.

• The Byzantines sent around 3000 men along with the crusade under the command of Tatikios and were involved in the battle of Dorylaeum. They left and went home before the siege of Antioch.

Basically they helped them very little and did their own thing, like retaking lost Anatolian territory when the crusaders had defeated the Seljuqs. They were very cautious of them and used them for their own ends and rightly so. Having an unstable army in the tens of thousands in near your territory is never easy.