If you can afford to wait, wait for the DS Lite. The screen is much bigger, and the weight is way lighter, with a better stylus (heavier and less cheap looking than the DS one). The only problem will be that gba cartridge will jut out somewhat... not a big problem if you're not planning to play GBA games on it.
Really, don't get the DS, now that the DS Lite is announced/ sold in Japan. My friends and I were all complaining like hell how difficult it is to hold and play the DS prolonged, because of the weight and size; and also how stupid that cheap piece of plastic they called the "stylus" work.
Think of DS lite as GBA SP and DS as GBA. The look is much better in the newer generation, as well as the size of the screen, the sound produced and the back-lighting...