The intel chipset automatically detects and configures your ram speed based upon:
Your FSB Speed
The rated speed of the slowest stick of ram in the laptop
could you make sure you have the latest version of cpu-z and post up a screen shot, I beleive cpu-z is reporting the base frequency and not the "quad pumped" frequency.
If I remember correctly i think it was possible to stick DDR-1 ram in the ram slots but that might have been just the previous generations of the pentium-m.
anyways Dell (to the best of my knowledge) has never stuck DDR-1 ram in the i9300. therefore only DDR-2 was used. and with DDR-2 the intel chipset for the i9300 can only select between 400mhz and 533mhz (based on the conditions I stated earlier)