Looks like the problem for me was two fold; firstly my indoor aerial whilst getting the signal strength was picking up way too much interference so gave effectively crap reception.   Grabbed a $100 worth of UHF aerial & pole from DSE and that cleans things up heaps (in fact we now have four extra non-freeview channels than before) - now to borrow a ladder from someone and get the thing bolted into place.

Secondly it appears that my 6600GS video card, whilst having hardware acceleration just isn't up to the task. So I'll be getting a 8500 or 8600 next week on order to take care of that.

Once installed by HTPC will be based on an Asus A8N-SLI MB, Athlon 3700+, 1Gb DDR Dual Channel, 1x320Gb + 1x500Gb SATA, decent quiet cooling all packed up into a Silverstone case.