Yes, the only way to get to 1GB of RAM (if your system originally came with 256MB) is to remove the 256MB of RAM and install two 512MB DIMMs.
Folks in the US market were pretty lucky when it came to this as “most” of the systems came standard with 512MB and only needed an additional 512MB for the 1GB.
All of the highend models come with 1GB standard.