You'd be bottle-necking on the internet connection with scrapebox with a dedicated desktop. If it gives you a better idea; I have an overclocked quad core, 8 gig ddr3 ram, raid 0, etc monstrosity and Scrapebox runs only slightly better than on my non-special "gaming" laptop.
If you do go the desktop route I would suggest a cheap (Possibly-overclocked) AMD quad core.. The reason behind this is you can leverage the extra cores and run a bunch of VirtualBox OSes for those apps that require "Full screen, front and center privileges" without gimping things.
....and you can just minimize (or toss on another monitor) the virtual OS and go about your normal everyday usage without interrupting the running program. Ram plays a big factor as well since you are essentially dividing up system resources with this setup. Just my 2c, if you don't take the VPS route. I do this on one of my machines.