Sorry if you don't want me mentioning the Apple computers, but for my daily routine, it's my main machine, but XNA is my programming environment so I just wanted to see if anyone here did this already.
While I have not extensively tested it on my MacBook with BootCamp (as I tend to use my desktop for coding), the early stuff I have done has come out very well with no noticeable issue with regards to graphics, that said I am yet to do anything really flash, however the included Spacewar starter kit appears to run fine so that may be a good benchmark.
Hope this helps!
For what it's worth, I am running XNA Game Studio Express on my iMac using Bootcamp and XP Pro, and it runs absolutely fine. That of course can be because it's got a 7600GT video card. However, I also have it installed on my notebook (Acer notebook, not a Mac) which does have an intel 950 graphics card. And even though it doesn't run at stellar speeds, it's ok for the games I am working on at home. Don't expect Halflife 2 type graphics, but for example Warcraft 3 runs fine on it, so it should be ok for a lot of homebrew games.
Obviously the Macbook Pro with the X1600 is the superior choice here, but it comes at a cost.. :)
Just as a data point, I use the cheapest White MacBook Core Duo non-Pro as my main XNA GSE hobby programming machine. I use XP SP2 with the standard Boot Camp device drivers. (I forget which version of Boot Camp I'm running; I think it's 1.3.)
The MacBook works fine for the simple 2D and 3D XNA games that I've written so far. And it has no trouble connecting to my Xbox 360 and downloading the games to run them on the 360.
In general the Intel 945G chipset used in the Macbook non-Pro is not too bad for graphics. While not as fast as dedicated GPU cards, it's certainly much higher performance than most earlier generations of integrated graphics. (I haven't kept up with Macbook models; a quick check of Apple's web site says the latest models are using 950s. I don't know how the 950 compares to the 945G, presumably the newer chip is better, but I don't know for sure.)
The one issue I ran into was that the 945G has some limitations on which features of DirectX it supports: I was stumped for a few days because I was trying to use a 32-bit index buffer, but the 945G only supported 16-bit index buffers. As a result, I didn't get any 3D graphics drawn on my display. But once I figured that out what was going wrong my 3D graphics worked fine.
Oh, I should mention that I have 1.5 GB of RAM in my Macbook. I don't know if that affects graphics performance or not, but it might.