I built my photo processing workstation back in '07...Windows Vista was new and didn't have a good reputation, so I settled with XP. Lightroom had come out and I had upgraded to Photoshop CS3.
I bought a 32-bit processor and installed 4GB of RAM and was quite happy with my setup. In fact, since I still use the older cameras from back then, well, I could still get by, except I figured I'd make the leap to the new 64-bit Windows 7, put in a new quad-core CPU, increase the RAM, and go with the Lightroom upgrade which was only good for a 64-bit OS.
Fortunately, when I bought the pieces for my workstation, I specifically bought a mother board that could be upgraded from the original dual-core CPU to a quad-core CPU, could handle the 64-bit OS upgrade, and that could handle a RAM increase. It has plenty of hard drive space. So, for a few hundred dollars I was able to make the leaps, rather than needing to shell out the bucks for a whole new system.
I'm presently using PS CS5 and Lightroom 4, not the newest versions, my budget is lately really tight, so I'm glad I had the foresight to plan ahead with my system! For people who want to delve into good camera gear and into the "digital darkroom", well, there are costs, don't buy the spendy camera and then go "cheap" on the processing gear!