Memory compatability question

[EvilCensor]

Just a quick question, the system I'm using atm is pretty old - a Gigabyte GA-8AENXP-D motherboard with a P4 640 (3.2Ghz).

At the moment the memory used on this system is DDR2 533Mhz 4300.. but I was wondering if I was able to use PC2-6400C5 800MHz DDR2?

Please excuse what may seem a pretty obvious question - but I'm way behind as far as hardware is concerned :/

[mrt9888]

Yes you can use faster memory, if you keep your old memory it will lower its speed to 533mhz.

[EvilCensor]

Okay thank you.. the manual says things like:

"Supports DDR II 711/600 and 533/400"

and..

"to use DDRII 711 you must install a 1066Mhz processor and overclock in BIOS"
"to use DDRII 600 you must install a 800Mhz processor and overclock in BIOS"

The P4 640 as I understand it is a 800Mhz processor, can anyone explain (from the scant info I've given), what kind of speed the new memory could or should run at?