Ram ddr2 533 & ddr2 667

can two different speed of RAM DDR2 533 & DDR2 667 can be used in the same PC?

Yes they can. Note: The faster of the 2 will slow its timings to match the slower of the 2. I.E. the 667 will run at 533.

(If you typed this into Google you would have had 19,000 responses in under a second)