Is there a way to replace Lucida Grande on Macs?

I'm a new Mac user, and I like Macs, but one of the reasons, oddly, for me not wanting to buy a Mac for quite some time is due to the system font, namely Lucida Grande. It appears everywhere - in the Menu Bar, the App names, and is the main font for almost everything, actually. I don't like it. I wish it was replaced by Helvetica. Just look at iPhoto. It's so neat, and the interface fonts is full of Helvetica.

I don't know why Apple kept embracing this font... Maybe it's due to its heritage? But the main reason I'm posting this is to ask about how I can replace Lucida Grande to Helvetica, simply put. I've tried using TinkerTool to no avail (it screws up the formatting and Lucida is only replaced in very few areas).

So has anybody tried to replace the system fonts yet?