I'm running Lion on 2007 MacBook, so it should support 2008 models.

The problem was with Mountain Lion, because it required 64-bit EFI (or something) which older models don't have.

Depends on which model and when you bought it. If it's an iMac, you're good all the way back to mid-2007. Mac Pro needs to be early 2008 or later. Mac Mini needs to be early 2009 or later.

If it won't run Lion/Mountain Lion, it won't run Mavericks either, unfortunately.

Also note that some features (e.g., AirDrop) aren't available on older machines running Mountain Lion, even if the basic OS runs. I don't know if that's been changed for Mavericks.

My girlfriend uses a 2008 aluminum MB (non-Pro), and I never had any issues upgrading her to previous versions of OSX. Now it's running Mountain Lion and downloading Mavericks as I type.