Is there any way to make an official iPhone app without installing Leopard?

Nope, you have to have the latest version of Leopard. Just go look for the developers’ page and look for system requirements.

Q: Does Apple allow you to _______?
A: No

Ivan, you’re gonna get scurvy as a side effect of your Self-inflicted Applitis.

Linux heals all wounds.

Furthermore, your Mac must run on an Intel chip. PowerPC-based Macs on Leopard are not supported for the iPhone SDK either.

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Apple provides a lot of good getting started info for iPhone developers here.

And you can download the iPhone SDK here.

Palm’s just released Mojo SDK for Pre apps is available for download on Windows, Linux, and Mac OS X.

But it still requires Safari 4 also.

If you want something tasty, it’s hard to get far from Apple.

Leopard is worth it by itself.
Or the Mac Box set. (= super deal).
Snow Leopard is coming out in the fall.