The AIC codec is not 'limited' to installing additional software. It is freely available on the web. All you have to do is copy 2 files in to the correct locations... (info also freely available on the web...)

AIC at PAL resolution on a G5 would be sufficient. You dont need to necessarily render at the DL1 native resolution (1024x768) - G5 and SCSI is OLD technology - although can still work with gentle persuasion.

I dont know what your budget is - but its worth getting a quote for an Intel Mac as a backup if plan 'A' doesnt work out for you... Do drop me a line.

Simon