I never thought much about this until I wanted to show someone how to use Adobe Lightroom. I thought it would be a simple task and that the person, who is also a photography enthusiast, would soon be exposed to the joy of digital image processing. Well, it didn't quite turn out to be the enjoyable experience I imagined it to be. I had severely underestimated all the other factors that are needed to implement a successful digital workflow. It doesn't matter what software you use; you need to have a decent computing environment:
1. You need a decent monitor. It doesn't have to be an expensive one, but it should have good colour reproduction, good contrast ratio, and a wide viewing angle. The monitor of typical medium-priced laptop is a good example of what you would want to avoid: the monitor is too small, and the viewing angle is quite narrow.
2. You need to have enough RAM. I am not talking about stuffing your computer to the max, but you'd be surprised how many people have just 1GB to run their Windows XP. RAM's are a cheap way to speed up your computer. Don't scrimp on that.
3. You need to do regular housekeeping on your computer. You need to do regular defrag, clean the registry, and delete unwanted files that build up over time. Otherwise, your computer will slow down over time.
From my own experience, digital image processing doesn't require a high end computer but you need to ensure that what you have will work properly (see above). My processor is a 2.66Ghz quadcore Intel Q9400 (cost ~AUD$600), running Windows XP on 4GB of RAM. Prior to this I was using a 1.6Ghz Intel Celeron E1200 with 2GB of RAM for my work.