Actually, 4 years is impressive in the hi-tech world, especially when the OS has changed substantially.
I, too, have an early MacBook Pro 2008 and came across this thread looking for info on whether I could install Mountain Lion on it. I'm disappointed, but not surprised, that it cannot be used--there are lots of improvements, many features (e.g., related to the track pad) that are CPU/GPU intensive or that work better with more recent hardware (big track pad, etc.).
I'm still running Snow Leopard on mine and it runs like a champ.
If you're still looking for a way to get into the ML world, consider getting an "inexpensive" refurbished Mac from the Apple store-- full warranty and you'll have a backup computer! (Use it for TV streaming-- or use one for travel, e.g., an MBA, and the other for home stuff, etc.)