Stability

• Always a sore subject for Windows users, stability has to be a consideration in choosing between these two. The winner here is Windows XP 64. The reason is simple. It's been around longer, so Microsoft has had ample opportunity to distribute service packs and patches to repair its problems. With XP now on its third service pack, most users are reporting it to be a remarkably stable 64-bit environment.
  
  

Memory Usage

• Physical memory is precious, and Vista needs lots of it.memory 3 image by Robert Molnar from Fotolia.com
  
  Windows XP and Vista both use tons of memory compared with their younger counterparts, like Windows 95 and 3.1. Vista is the bigger memory hog of the two. Vista leans more toward the eye candy, with brilliant graphical presentations and transitions. For this reason, it can definitely consume more system RAM than XP does. Of course, this can all be turned off if you like, so either can be refined to your taste and memory.
  
  

Drivers

• For the same reasons as stability, XP has a better pool of hardware drivers to draw from. While Vista has a rich library of drivers that make it compatible with most anything you try to use it with, the drivers for XP have been updated and retooled. They are more mature. So, depending on the nature of the hardware devices you'll be using, you may want to stick with XP. If you are investing in all new hardware anyway, Vista's drivers will be just as young and good as that of XP.
  
  

Hard Disk Space

• Windows Vista finances its memory needs with virtual caches on the hard disk. This is a method that has been used by operating systems for years now, but Vista takes it to a new extreme, sometimes using up to 15 GB of your hard disk for memory operations. XP caches as well, but nowhere near this amount. If you have the latest supercomputer with a terabyte of hard disk space, this may not concern you. However, if you are making do with an older system with a more modest drive, XP may be your answer.
  
  

Price

• The real question between these two operating systems is whether the price to upgrade is worth the extra bang you will get for your buck. In this case, with XP sometimes outperforming Vista, it comes down to personal preference whether its worth the money to upgrade at this time or wait until Windows 7 gets settled in. On a lower-end system, your computing experience will probably be more efficient and pleasurable with XP. On a higher-end system, Vista may be worth it for the extra bells and whistles.