As I have installed Windows 8 on different computers I have access to I have noticed that it runs well on hardware that came with Windows Vista or newer. The Dell Inspiron 640M is an exception to this as it came with Windows XP but was supposed to be Windows Vista capable. I would say that faster Windows XP machines will run Windows 8 well.
As for this install, I did a clean install of Windows 8 Enterprise. The install went well without any issues but there were a few drivers missing, now first run Windows Update as this will install a few drivers then there will only be two more that you need to install. The first one is the Ricoh R5C832 which you can get from Dell’s support website. This will install all but one device wish is a video device, now Windows Update may have installed it but in my case it did not. You can grab the driver from Intel’s support website. It is for the Intel GMA 945 and you want the one from Intel’s site not from Dell’s site the Dell one will not install in Windows 8. After you install these you should have a clean Device Manager.
Overall the system does not run bad, you can tell it is an older system and a ram upgrade would probably do it well. I would say that this machine that came with Windows XP and was Windows Vista Capable is also Windows 8 Capable. This is great for light computer use like Facebook, e-mail, photos, and just general web use. I even was watching online videos without any issue. Below is the Windows 8 Experience Index. I also ran the Passmark Performance Test and the machine gets a 411.8.
These Vista Capable computers I think as a rule of thumb are as old as you want to go for installing Windows 8. Those of us that are tech enthusiast will want to install it on older hardware but so far I am not sure I like Windows 8 on older machines than this. I would suggest it on this machine, though, it really does run well.