You are right to say that your MacBook has a lower-grade graphics card - you have the same card as is in the Mac Mini, an Intel GMA 950 which has the ability to share only 64 megabytes of your system's main memory - likely to be one, or possibly two gigabytes in your situation, however to get such a poor performance I'm guessing you only have the then-standard one gigabyte of memory.
Whilst this shouldn't tax your system too much it appears that it is doing just that to the extent that the graphics suffer. I have some good news; you're not alone. My Mac Mini does exactly the same thing. There is bad news unfortunately; I haven't come across a fix for it yet.
The new MacBooks and the MacBook air ship with the Intel GMA X3100 which has the ability to share up to 144 megabytes of system memory with the computer, and all but the lowest MacBook now ship with two gigabytes standard system memory. When I get my MacBook this week, I'm upgrading to four gigabytes immediately - mainly because I plan to use Final Cut Express every so often.
I'm sorry that I haven't been able to help with the problem but perhaps explaining whats wrong might have helped a little.
Dæmon
