I'm Running Intel Core Duo 1.86 Processors, 3G DDR2 660 Ram with Vista and XP on separate partitions.
Vista is fine for video editing but I'm personally not happy with trying to use avi-synth just because of the fact its just wont recognise notepad as its default program to open up with.. thus I use XP, I know it will work.
Rendering with XP.
With the above specs I find rendering 1500 frames with 3 layers of effects and wav audio in premiere pro to take about 3-5 minutes to complete. The advantage is that the duo processors will allow you to alt tab and work on something else.
Be aware though that if it too uses a lot of processing power your render will complete but die in the arse.
Rendering with Vista.
As states above except it handles the alt tabbing a bit better, I can actually alt tab between several documents and the interwebz maybe even watch a video/dvd while it render's, haven't had a problem yet.
Core Duo was created for multi-tasking, break her in until she bleeds, then you know how far you can go until it falls over =/