Question for the PC gurus......

My PC is about 4 years old and hopefully I can get another year or so out of it. It has a 2.4Ghz Pentium4 processor with 512M of DDR SDRAM. I am buying some more memory but want to clarify a couple of things first.

There are 2 memory slots and according to the technical documentation it will take either DDR 266 or DDR 333 memory. The 512MB I already have is DDR 266.

1) Do I need to install exactly the same speed of memory in both slots ?
2) The system bus is running at 532 MHz. So which speed of memory is optimal. If I buy the faster memory will I get the full benefit or will it be restricted by the system bus speed.

Thanks.