Read http://en.wikipedia.org/wiki/DDR_SDRAM The DDR clock rate is half the data rate. Hence 333MHz DDR runs at 166MHz clock.
and googled this:
All Kingston memory modules must perform properly to ensure maximum performance. Therefore, Kingston has developed an industry leading quality process to ensure that Kingston memory delivers superior quality, performance, and 100% compatibility with the computing system the module is designed for.
General Information
Manufacturer Kingston Technology
Manufacturer Part Number KTD4400/512
Manufacturer Website Address www.kingston.com
Product Name 512MB DDR SDRAM Memory Module
Product Type RAM Module
Technical Information
Memory Size 512MB
Memory Technology DDR SDRAM
Number of Modules 1 x 512MB
Memory Speed 266MHz
Physical Characteristics
Form Factor 184-pin
Warranty
Standard Warranty Lifetime Limited