okay, lets spell out somethings here.
microsoft has developed these operating systems for key market groups.
windows 2000 - designed for small business use. can be used as a server. complex setup (although not as bad as NT4) and maintenance. extremely stable. extremely compatible with previous versions of windows.
windows 2000 server - essentially the same as windows 2000 but with a lot more back end support for multi-ring networks. more supportibility for DNS and WINS networks. designed for use with multiple server boxes.
windows XP home - designed for the home user. windows XP uses the basic kernel as windows 2000 so it is relatively just as stable. windows media player built in for ease of use. in a nutshell, this has all the perks necessary to garner the interest of the average home user...those being...ease of setup, simplistic file management, built in support for various file types using microsoft products (which are thereby easily updated through windows update), a built in firewall...etc etc
windows xp pro - essentially the same as home, but with more windows 2000 services built in. meaning more control in a multi user environments.
all three are stable operating environments, with distinct advantages based on what market group you fit into. if you are the type that is looking for a plug and go kind of operating system, XP home edition is for you. if you're a power user that has a lot of experience in windows environments, then Windows 2000 will suit you perfectly. if you find yourself somewhere in between....XP pro or 2k are both valid choices...but I'd stay away from XP Home Edition.
2k server really is a business operating system. unless you are running a large amount of information through a network in your home...I really see no advantage that win2kserver has over plain old vanilla win2k.
there is a cost difference in any of these operating systems if you buy an upgrade or the full version. my take on it is this: if you have any previous version of windows
buy the upgrade. the upgrade is the full version of the operating system, but it requires another windows cd to use! ie., if you buy XP pro upgrade and you already own Win98, during the install of XP it will ask you to insert a cd from a previous version of windows. stick in your win98 cd and it will recognize that...allowing you to continue. so, to re-iterate...if you own any previous version of windows, buy the upgrade as it will save you money!
hope that helps with your question, and sorry if I got too carried away.
ohhh...side note. all those comments about winxp having too many "pretty fx" that slow down your computer? all of these things can be turned off. so do not let that sway your opinion of which operating system you feel is right for you.