Can Windows XP Professional Be Upgraded To Windows Vista?

Vista requires lots of memory and disk space.  I would recommend at a minimum 1G RAM and 50G hard drive.  If your CPU isn't dual-core or 2.5G plus you probably won't want to do this.  Your video card needs to be late model and preferable high-end (256M+).

More than 50% of my friends doing this upgrade have regretted it. Most of them have had to completely reinstall - all installed software was lost.

My advice is to use your computer until it breaks down and then buy a new one - with Vista if that's what you really want.

Yes, but I don't know any reason to do so at this time.  Your hardware requirements are much greater with Vista than with XP and as such you will see much longer boot times, etc.  At a minimum, I would wait until the first Service Pack comes out (which is supposed to be soon).  As long as XP is meeting your needs, I know of no good reason to upgrade.

It can be done, if your pc specs match the hardware specifications that vista requires.