RAM

hi gents,
I have an easy question for you computer experts.
My PC is running pentium 4HT 3.4GHZ, LGA775 socket and FSB800. the memory I use is DDRII PC3200.
the question is can I use PC3700 or PC4XXX instead PC3200?
this question is because I can have RAM for a very competitive price but nothing in PC3200, just of higher bus frequency.
also, can I mix PC3200 RAM with RAM of higher bus frequency or do I have to only use the same frequency for any RAm installed?
What would be the consequence of running RAM of higher bus frequency than the computer, or mixing RAM frequencies?
well, I said one question, it's actually 3...
thanks for your help
I have an easy question for you computer experts.
My PC is running pentium 4HT 3.4GHZ, LGA775 socket and FSB800. the memory I use is DDRII PC3200.
the question is can I use PC3700 or PC4XXX instead PC3200?
this question is because I can have RAM for a very competitive price but nothing in PC3200, just of higher bus frequency.
also, can I mix PC3200 RAM with RAM of higher bus frequency or do I have to only use the same frequency for any RAm installed?
What would be the consequence of running RAM of higher bus frequency than the computer, or mixing RAM frequencies?
well, I said one question, it's actually 3...

thanks for your help