Check 'About this Mac' under the Apple icon, then select More Information. Click on Memory to see what specification of memory you currently have, and make sure you match those specs.
IMHO you don't need to match manufacturers, although some people will tell you that.
You can also use the memory compatibility checker at www.crucial.com to make sure you order the right upgrade.
Just a thought, if your current 1GB consists of 2x 512MB DIMMs, which is pretty common, then you may need to get 2x 1GB DIMMs
you could get a 2GB stick to make it 3GB, though you won't have dual channel support, i think the extra GB would make up for that.