well, I would suggest to take out the 512 Module: it will most probably not slow down Captureshop, in the contrary. Leaving it in will give you physically more Ram, but not making it necessarily faster, sometimes even being the cause of crashes. It is our experience that the same modules (AND SAME brand) of Ram does improve stability, especially with "Ram-hungry" applications (not only Captureshop).
As an example, I can speak about my own experience in a customer's place, where we had a mix of 256, 512 and 1 GB modules (total 2.5), with which we experienced crashes from time to time: after having taken out the 256 and 512 modules, the machine was FASTER and did not crash anymore!
I have just got the borrowed computer. The Macbook has one Module Size:512 MB Type:DDR2 SDRAM and one Module Size:1 GB Type:DDR2 SDRAM; should I expect any problems? Why it is so important to have the modules of the same size?
Sorry for my ignorance.