Enter the Gateway system model, etc., and it will tell you what memory it recommends for the system.

Also, look at the chips on the SIMM you have. One string of long numbers will tell you what the actual RAM chip is. From that number you should be able to figure out what the actual SIMM is using and whether it is 16 MB or 64 MB.

[link|http://www.arstechnica.com/paedia/r/ram_id-2.html|Here's] and ARS Technica article which talks about identifying SIMMs. There's other stuff out there as well which a Google search will turn up.

HTH. Good luck.

Cheers,
Scott.