The first thing people usually notice when they make the transition to Window's Vista is that it uses half of your memory without running any programs.  If people are like me, my first assumption was, "Geez, Vista is a memory hog!  I should go back to XP!"  Upon further investigation I realized my frustration was just from a lack of knowledge than any fault on Vista.

This hub will explain why Vista uses half of your computer's memory and how that is actually a beneficial thing for you.

Windows came out with a technology in Vista called Superfetch. Superfetch basically seeks to speed up the performance of your computer by learning which programs you use the most and then preloades those programs. This means less waiting time whenever you go to open that program. This is great for the work flow, but totally kills the beloved "coffee break".

So for example, I use Photoshop and Mozilla Firefox often. Vista will notice this and actually preload those programs in the background. This creates a noticable difference in the programs you load often to the ones you load only occasionaly.

In addition to preloading your most used programs, Superfetch also optimizes the computers updates and defrags to run at times that won't interfere with your work.  In the words of Microsoft:

Windows Vista also runs background programs, like disk defragmenting and Windows Defender, at low priority so that they can do their job but your work always comes first.

So to relieve your worries, no Vista isn't a horrible progression from XP.  It will always use half of whatever memory you have in order to boost the performance of your applications.