Open up activity monitor, check the number of page outs, report that number back here. That number is reset every time you shut your computer off, so tell me how long it's been since you've completely shut it off as well.
Also, can I get more specs? If it's just a Macbook, and not an MBP, you can upgrade it to 6 GB, not 8. Even if you stick 2x4GB sticks in there, your processor (which can't be upgraded, soldered in) will only utilize 6GB.
Granted, 6 GB should be enough for what you're doing. Hell, 4 gigs should be enough, but in order to accurately figure that out, we're gonna need some more info. Specifically, make sure you're telling us your exact processor. The latest Core Duo Macbook (maybe it's Core 2 Duo, there's a difference) was last sold in 2006.
Unless you've got the Unibody macbook (you'll know it's unibody if you've got the GeForce 9400M graphics card)
If you've got that Mac I've just described, then, yes, you can fully utilize all 8 gigs of ram, provided you've got snow leopard + installed, which you do. Depending on the page out size, you might see a performance increase.