No point going to Feisty - go straight to Gutsy.
If it were me I'd be dual-booting it - I don't know what the wireless broadband support is like in Ubuntu, but history of the way things are done by the telcos in Aus would make me a bit wary.
If you get it to all work, you can always just mkfs the Vista partition later, and use the space for your mp3s or videos or somesuch.
Use the Vista disk manager to shrink the NTFS partition - it's very good. Can't say that about any of the predecessors.
(didn't even know Moonta had a bay ...
)