This excerpt taken from the ATVI 10-Q filed Feb 8, 2006.
4.7.1 All Title Updates for Software Titles are subject to approval by Microsoft. Publisher may releaseone Title Update per Software Title free of charge. Any additional Title Updates proposed by Publisher may be subject to a reasonable charge.
4.7.2 Microsoft may require Publisher to develop and provide a Title Update if (a) a Software Title or Online Content adversely affects Xbox Live, (b) if a change to the Xbox 360 Publisher Guide affecting Online Content requires a Title Update, (c) if Certification is revoked for Online Content, or (d) for any other reason at Microsoftsreasonable discretion. Microsoft will not charge Publisher for the Certification, hosting, and distribution of Title Updates to Xbox Live Users for the first Title Update (if any) per Software Title or Online Content required by a specific change in the Xbox 360 Publisher Guide or for any other reason at Microsofts reasonable discretion. Microsoft reserves the right to charge Publisher a reasonable fee to offset the costs associated with the Certification, hosting, and distribution of Title Updates to Xbox Live Users that are required because of revocation of Certification or a Software Title or Online Content adversely affecting Xbox Live.