Well, the MSI board uses DDR. Wether your first system can accept it depends on what type of RAM it accepts. If it doesn’t accept DDR, then no. If it does, it should work.
The MSI board can accept up to 4GB with 4x 1GB DDR sticks.
Yes. However, like most motherboards these days, it’s equipped to handle 2 memory controllers, commonly referred to as dual-channel. This requires the same amount of RAM in each channel. It tends to get a little tricky when you use an odd number of sticks. It won’t damage anything, but you might hit a few minor bumps.