my system was actually fine.
Whilst rendering which is exactly what BURP does frame by frame most pressure is on the total RAM to store it all and then process it.

My machine was working as usual for standard operations - just email and browsing.
Just to push my machine and see what would happen i opened a few graphics and applied effects (to 2048x1024px images) and then it was slow. I will proabably just run BURP when i am not at the machine (depending what i am doing).

-- you could always apply the wait 3 minutes of no user input before starting BOINC