There's nothing wrong with the 12-inch iBook, but I would recommend going for the mid-range 14-inch iBook if you can afford it - the one with the Combo drive, not the SuperDrive. It's a little more expensive, but I think if you have used a laptop before with a screen size larger than 12", you're going to find it to be too small.
I used a Toshiba Satellite S155 for two years with a 14.1" viewable area, and when I went to an Apple retailer to check out the 12" iBook, I was stunned. I was squinting to see things. I would have been really quite unhappy if I had gotten one that small.
Really what you might want to do, in this case, is to go to an Apple retailer - if you can find one - and check it out in person to see if the size is what you're looking for. I think there are some very inexpensive PC laptops out there that are similar.
One such laptop you might want to check out for a rough comparison is
this Averatec model. It's got a 40GB hard drive, 12.1" screen, 256MB RAM, and an AMD Athlon XP 2000+ processor. It's a rough equivalent, of course, because there's no real way to make a genuine direct comparison between a Mac and a PC.
I think it's pretty much safe to say that you'll be paying more for the Mac, but you will probably have fewer headaches and, in my experience, get more work done. I read a good quote once about this particular phenomenon: Mac owners use their computers, and Windows owners put up with their computers.
Best of luck to you.