Memory Upgrade DDR2-6400

[Unicorn]

Will my motherboard support these sticks for a start
Corsair XMS2 4GB (2x2GB) DDR2 PC2-6400C5 TwinX Dual Channel (TWIN2X4096-6400C5C) [TWIN2X4096-6400C5C]
http://www.overclockers.co.uk/showproduct.php?prodid=MY-190-CS&groupid=701&catid=8&subcat=813

My motherboard is an ASUS M3N78 which currently has 2GB DDR2-6400 @ 800 installed and it runs fine but i want some more kick out of it

Is it worth it also?

Fast replies appreciated as i want this free shipping

 

[Unicorn]

I don't know were to buy used memory to be honest. Were is safe from and reputable.

 

[Unicorn]

found some for 30 but the seller only has 1 feedback nd that's buying not selling. should I risk it ?