What are your FSB and multiplier numbers? (166*11 ?)
i may be wrong, but if your FSB speed on your processor is set at 166MHz then you would only realize 333MHz form your RAM (PC2700).
go into your BIOS and set the FSB speed to 200MHz and reduce the multiplier to 9. This should get your RAM to run at 400MHz. then, if you want to, you can increase the multiplier (9 to 9.5 to 10 to 10.5...) to see where your Processsor tops out at. this will mean that you're overclocking the processor. Hope that helps.