The Startup Manager won't show with Option key pressed?

Today I've taken the curious step of attempting to downgrade my 10.7 system to 10.4.

This led me to create a new partition and copy onto it the startup disc for 10.4 because my MacMini does not a drive slot. And sharing the disc from another machine didn't work either (it wanted to restart using that drive as a startup disc but that wasn't going to happen).

I set the Startup Disc as this new partition and chose to restart. I perhaps should have just double clicked on the installer... Hindsight, where is it when you need it?

I get the bong, I get a lit screen... but that's all I get. No apple icon. Just cicadas. And after an hour or more, no change.

So, I try repowering the Mini with the option key down and that no worky either.

Any suggestions?

Would setting up a thumb drive as a startup disc help at all?

Thank you in advance.