In a word, no. There is Mono support for the iPhone, but it's currently limited. They have spoken in the past about the possibility of writing a Silverlight app, with a series of "iPhone style" controls that could be statically linked as an iPhone app, but that's some way off.
If it's games you're interested in, and you have deep pockets, then UNITY[^] is a Mono based game development platform that supports the iPhone (and runs on Windows)
Failing that, bite the bullet and get a cheap Mac from EBay. Officially only Intel Macs are supported for the SDK, but you can get it to install on PPC ones and I've yet to have a problem with that (I'm running it on a G5 PowerMac at the moment)
MonoTouch[^]. You still need a mac and a minimum of $400 (as of this writing)
You can try the evaluation version which doesn't require you to pay and allows you program using the simulator. If you want to test your app on the hardware then you need to pocket the money.
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