I see u are from germany so i searched German network for computers and what do ya know:
102 euro
so it should be better for you than dual core
second thing mainboard: i couldn't find in german network cuz it's all there in the language which i dont understand so i searched my own network for a AM3 and ddr2 compatible mainboard and i found this: GIGABYTE GA-MA790X-UD3P try searching it in ur country maybe u'll find and i'm sure there are more of these mainboards which support AM3 and ddr2.