IIS Performance

Hello,

I am testing a product my company is producing, and i have a load testing tool...when i load up to around 100 Users simulataneously onto a Windows 2000 Server running IIS 5.0

(This Server has Win2k,SQL 2000 Only - This Server is a Dual AMD 2200+ Processor, with RAID 5)

IIS Starts occassionally returning the message: "Server Busy"
I have turned the site performance up to over 100,000 Visitors per day but still with no affect...any ideas of how i can shift this or is it a Microsoft Problem?

Thanks :D

Chris - MCP :)