The PowerBook G4 Titanium can be upgraded to 1GB by adding a 512MB module to the existing 512MB (If you have the 256MB from the factory, remove it and install an additional 512MB for a total of 1GB)

Standard Memory
512MB Removable
Maximum Memory
Memory Expansion (No. of sockets)
2 Expansion Sockets
Memory Expansion
Install 1 at a time
Memory Sizes
128MB | 256MB | 512MB
Memory Speed (Type)
PC133 or PC100