I'd wait for the PS3. I have a Xbox360 and I'm more than happy with it. But if I had to decide between the two I would have to go for PS3. Why ? The gamelineup.
Imo the PS3 will dominate the market again and therefor the variety and amount of great games will be higher again. Especially if you like games from japanese developers...Gran Turismo for example...
The PS3 won't be out untill Christmas/Spring (again, last time I cared to read about it) so if he starts saving his money now, he can get the XB360 for his birthday and then buy a PS3 when it comes out and have the best of both worlds.
I've got a handful of friends that have 360's. They're planning on returning them for the PS3, when it's released. They say it's not really worth the money, unless you need a nice dvd player.