I'd like to know if you think the white MacBook (2.26ghz, 2gig ram) is sufficient for software development (using Xcode, Interface Builder etc...)
To elaborate on @Martín's answer, a MacBook is perfectly fine for development, I use one myself and never had issues.
But you could improve it. Switching to 4GB of RAM would be first thing on the list. Using a second screen could also vastly improve this setup. Another (bigger) investment would be to buy a SSD.
XCode 3.x (and possibly 4.x when it's released) will definitely work on that Macbook. I have an old white Macbook 2.4 Core 2 Duo with 2GB of RAM and it works. Compared to the 8 Core Mac Pro, it's really slow, but it's fast enough to use it and do things with it.
If you want to compile a big and complex project, it will of course take longer, but other than that, the hardware is perfectly capable of running Xcode and its surrounding tools.
The projects will take longer to load after a cold boot, and the whole machine is naturally more limited in terms of absolutely everything (compared to a regular Mac Pro, iMac or even a newer Macbook/Pro), but if you need a light and loyal machine, this will definitely serve you.
I'm using mine with Mac OS X 10.6.6. I remember even playing World of Warcraft on that machine a year ago.
I own a white MacBook (MacBook4,1) with the 13" screen. I got the RAM upgraded to 4GB right when I bought it, so I unfortunately cannot say whether 2GB would be sufficient for iOS development. However, with 4GB, I run a low-profile Linux VMware Fusion VM for development, and also XCode and IB, and my system runs fine for the most part. Over the years, it has become a bit slower, though.
I'd like to point out that the 13" screen may cause problems. While it is an amazing screen in terms of display quality, it is sadly pretty small for most development stuff. I am not saying you cannot get anything done. You can. I did for over two years. But it cuts down on your productivity. In the case of Interface Builder, you will quickly feel the constraint as Interface Builder is fond of spewing countless Windows all over the place. A second display is going to help a lot, but you may probably not be able to get exactly the same quality of display on the external as you would on the laptop screen. It is something that gets to me from time to time.