Motherboard Memory Limitations

digitalunity asks: "When most motherboards with room for 3 DIMMs state their maximum memory as 768MB, it would seem that this is based upon the assumption that a 256MB DIMM is the largest available. I noticed that IBM has said that 1GB DIMMs will be available soon. Are the stated memory limitations of motherboards inherent to their design or can you really put more memory than they state?"