Adding Ubuntu to the mix...

Ok, so now I have my iMac set up with Snow Leopard and Win7 x64 bootcamp. So far, so good. But what if I wanted to add Ubuntu to the mix ?

I've learned that a triple boot system is not so easy to set up. However, I recently installed ubuntu 11 on our dell laptop using the wubi installer. This installs Ubuntu just like any other app on a windows machine (in our case win7 x64). When booting, you have a choice between booting into windows or ubuntu. But I suppose that this could interfere with bootcamp and mess everything up. Or not ?

And what about booting Ubuntu from a USB key ? Is it possible on a Mac ? Anyone tried this and how fast is it (is it workable ?) ? Can you partition a USB-key ?