Read this , it will help you find the queries that are causing this high load. When you found them maybe you can remove them or run them cached.
Whoo Reviewed by Whoo on . high load of vb-mysql on my server hi on my vb forum i have only 100-200 ppl online sill my mysql database is using 350-390% load out of 400% load its really annoying making my site slow my server details:- cpu speed/type single or dual cpus): 2 x 2.8ghz xeon how much memory installed: 2 x 2gb ram hard drive type/configuration: 2x 72GB 10,000 RPM SCSI linux distributor or windows version: CentOS 5.3 i386 apache/IIS version: Apache/2.2.3 PHP version: 5.2.6 Rating: 5