Just going to make this short and simple, there are many places, including Microsoft documentation, which state you can set the event log size up to 4GB.  While this is true, it will never get remotely close to reaching that size, or 1GB even.  Due to some very bad design, the event log uses memory mapped files under the services.exe process, which due to another very bad design, is limited to 1GB pool.

http://www.microsoft.com/technet/security/guidance/serversecurity/tcg/tcgch06n.mspx

This apparently is not an issue in 2003 64bit, and is resolved in 2008.