SQL Server Performance

Any other solutions to improve performance besides adding RAM? I have an application that accesses SQL 2000 running on a dual Xenon 2.6ghz processor with 2 gigs of RAM. DB size is ~ 9 gigs uncompressed, sometimes access is immediate, sometimes it can take 3 or more minutes. I can’t say it’s a network problem as even if I run the application on the SQL server I can get varying response times.