Acer did not produce those motherboards, ECS made the 661GX-M7
Here is the Manual :
https://www.manualslib.com/manual/453011/Ecs-661gx-M7.html
so looking at the specifications on page 8 it clearly states;
and regarding RAM memory;
searching deeper for answers on CPU-Upgrade web site :
http://www.cpu-upgrade.com/mb-ECS/661GX-M7(V3.0).html
you can see clearly the ONLY cpus known to work on this motherboard and NONE of those include any Duo Core2 series CPUS
finally the web site of the manufacturer confirms all of these previous details
http://www.ecs.com.tw/ECSWebSite/Product/Product_SPEC/EN/Motherboard/661GX-M7%20-LL-V3-DO-0-RR-/Socket%20775%20-LL-Intel-RR-
CPU
LGA775 socket for latest Intel Pentium 4 / Celeron D processor
FSB 533MHz
Supports Hyper-Threading Technology CPU
and final nail in the coffin on the subject the manufacturer has a lovely list of CPUS you can use on this motherboard
http://www.ecs.com.tw/ECSWebSite/Product/Product_Support/EN/Motherboard/661GX-M7%20-LL-V3-DO-0-RR-/Socket%20775%20-LL-Intel-RR-