I upgrated from win2k pro to winxp pro couple of days ago.
The installation goes smoothly and takes around 40 minutes,

The first thing that i notice is the more "comfortable" log on screen for users of the computers , instead of having to press alt-ctrl-del and write your user name and password it now offers you a menu interface were a user can see all the user names of the computer and simply click on the user name he wants to log on (needing the password of course)
This is something i did not like since i always log on as administrator on my computer and this menu only offers users other than administrator to log on.
But it is possible to change that and get the "old" win2k logon,actually you can customize winxp to have the excat look of win2k but that does not make it win2k

I log on as one of the other users of my computer that has admin rights and see a totally diffirent look of windows , they have now installed skins, the default skin (and the only one that comes with windows) is beutiful but way to bright for my taste. I then decide to see what other skins are available and find that windows only offer this one skin, you have to buy the microsoft plus package to get more skins.

There have been a few software incompatibilities and one hardware incompatability after this installation , the software that did not work is "Ctlauncher.exe" (that is the program that comes with soundblaster live soundcards and sits on top of your desktop allowing you to change the volume and other stuff regarding your soundcard, in case you didnīt know)
I went to creative.com to check for upgrated, win xp compatible program but did not find any... well no biggie i thought iīm sure they will make a compatible program soon.

The hardware problem i ran into was an USB problem (what else) my system has always had USB problems until i installed win2k
from win98SE, but now with Winxp i again have to plug in-and out my usb mouse every time windows starts to get it to work.

The integrated burning in winxp is nice and it also has built in firewall but that firewall does not prevent programs on my computer to access the net like zonealarm does so i am forced to have zonealarm installed wich makes the firewall that comes with winxp useless since i want to control what programs can access the net and two firewalls are a waste of memory.

My conclusion : WinXp is simply microsoftīs way of saying do not use non-microsoft software, buy our os and we will fulfill all your software needs , our new os comes with skins(that you have to buy) a firewall(not a good one) a program to edit movies yadyaydya .....
My adice : Donīt upgrate , there really is no reason, not yet at least.