OK windels, you won. I forgot the update didn't come until 2009. You win 2 chocolate internetz.
Your MacBook Pro supports 4gb officially by Apple, however it is reported to work with up to 6gb using 1x4gb chip and 1x2gb chip. I highly recommend you speak with someone who has tried the second option before doing anything stupid. Nothing's worse than trying to return ram for incompatibility.
I'd recommend going with 2x2gb sticks =\ Trust me Snow Leopard handles it fine, it runs GREAT on my 2.4ghz MacBook aluminum with only 2gb ram. I have a feeling your beachballs are due to the hard drive. Have you installed all of your Software Updates? Go to the Apple and click Software Update.
If you are up to date and are still experiencing beachballs there has been an influx of calls to Apple for the same issue on the same or similar machines and they will likely offer to replace the hard drive.
Also: The build number is the version of the software you're using