Will a DDR2 2 GB RAM module be compatible with my existing DDR2 1 GB?

Will a DDR2 2 GB RAM module be compatible with my existing DDR2 1 GB?

I use an old system with a G31D-M7 motherboard with 2 DDR2 memory banks.
The module I plan to use is a 2GB DDR2-667 type. I'm sure my existing
module is a 1GB DDR2-667 too. The Brands are not same.
I understand maybe having two identical 2 GB modules and possibly
upgrading my motherboard would be the optimal solution but in my scenario,
that's not possible. So kindly tell me if these two modules will get along
in my motherboard.
Also, do those need to be slotted correctly or can be slotted in any order
I desire?