couple questions about my computer

ok i have a 512 mb 333MHZ and i heard its not good to mix ram speed like ima buy a 512 MB 400MHZ will it mess up my pc????

and i have a intel pentium 4 processor with HT and my pc has massive heat coming from it and i have 3 fans 1 from power supply 1 from processor fan and 1 for exhaust fan and i want to install 2 more fans 1 for side and 1 for front and i dont have any more places to install fans my power suplly is a Antec 2.0 True power 2.0 its a 430 watt and will i be able to install 2 more fans and were would i install the fans??

The P4 HT series run REAL HOT. One of Intel's downfall of late. You can mix the mem i believe BUT you will not be running at 400MHZ the mem will run at the lowest speed of all the sticks. 3 fans should be adequate but if you are out of spots to install your fan on your case then you are SOL if your not brave, if brave then make 2 mounting holes for the fan. I'd put one on the front to improve airflow. One on the side is overkill IMO. One thing you can do to protect your processor is to replace the thermal compond between your CPU and Heatsink/fan. Only do this IF you are computer hardware savvy. If you are go to newegg and buy the arctic silver thermal compound...you'll be amazed at the difference in CPU temp. That's all we use here now on our custom built pc's.