DDR3 is what you need for that mobo. Why do you need 32-bit Windows? Do you have exotic hardware or old programs?
4x1GB will run in dual channel mode, with 2 RAM modules per channel. 2x2GB will also run in dual-channel mode, with 1 RAM module per channel. 1 channel is one pair of same-colored RAM sockets. So if you have four RAM sockets labeled red, blue, red, blue, then putting two 2 GB modules in the red sockets will run them in dual channel mode. In my opinion, you should go for 2 GB modules instead of 1 GB ones. That way, you can have a larger RAM pool if you fill up all slots.
I suggest you get 2x2GB and get Windows 64-bit. If you already have a license key and the 32-bit installer, you can simply download a 64-bit original Windows 7 ISO and use your key. That should work fine.