if i want to increase my pc ram from 256 speed 266 to 512 speed 333 will it cost any problem?

Answer 1

If you use the same type (speed, pin count and the latency is close) more ramm is better. You can put a slightly faster speed in wth no problems, it will throttle down to match the slower chip. Use a memory configurator like at crucial or kingston

Answer 2

No, your computer will run the 512 Mb of RAM at a speed of 266Mhz not at 333Mhz.