Hi
Not sure if this is any help as I don't use motion, however I am using FCP. I live in Australia too, I bought an e-mac with superdrive for around $1500. It has 80gig hard drive, and I think the new ones (mine's about a year old) have 1.25gig processor and you can get up to 1gig ram. Mine has 1gig processor and 512mb ram.
I find it works pretty good but not doing anything too complicated with it, just straight editing, e.g. no special effects.
The 80gig is really limiting though, so I bought an external Lacie hard drive, which works okay though I think it seems to be a bit slower when you edit to the external but not sure, I would prefer more internal hard drive but told not possible on the e-mac.
The only real problem I have had is I did an idvd project which was very slow on my external hard drive, so switched back to the internal drive and was okay, but have been told that idvd has lots of bugs so this may be an idvd issue (have found a few bugs myself in idvd).
emac only has firewire 400 compared to other macs (which I think have firewire 800) I really have no idea if this makes any difference though, but makes me wonder if that is why my external drive is a bit slower, but it could be due to my lack of ram (have been told conflicting things by apple people some say lack of ram makes it slower, some say 512mb should be fine.
I considered buying the mac mini but it has similar limitations re hard drive size.
If you can afford it get something with more hard drive size than 80gig, but if you a bit broke than the emac (and possibly mac mini) might do the trick if you add an external hard drive. Other than hard drive space I am pretty happy with my emac. (though lack of portability can be an issue too).
We used to use a 6gig imac (you know the turquoise looking ones like the one you have) and you won't believe the speed once you starting using the emac.
Interestingly I was always told to edit directly to internal hard drive as faster, but I belong the screen editors association and one of the editors there (who had worked on many docos)said she always edits to external hard drive due to portability and has no problems.
Please keep in mind though I am a semi-professional film maker(e.g. make short movies/docos for film festivals), not a full professional, so my opinion may not be the best informed.
By the way I found an australian apple forum site which might be helpful called
www.appletalk.com.au