The short answer: No. The long answer: read this post from Steve Yegge, who delves into a lot of the Mac design philosophy and his trials trying to get x-mouse-activation working on his Mac.
While x-mouse-activation (focus-follows-mouse) will do what you mean to do, it's apparently unsupported at this time. I recommend Linux. I end with this quote from the referenced post:
Apple OS engineers don't want you to do stuff that they don't want you to do, and they specifically define "stuff they don't want you to do" as "stuff they don't think you want to do." This is actually endemic to Apple forums in general. Whenever someone says "I want focus follows mouse behavior!", some people inevitably reply that "you really don't want to do this". It's that whole "we designed it the right way for everyone" mentality that turns off so many would-be Mac users.