If you are just wanting it to test KDE4, you can get slackpacks for kde4 to allow it to coexist with kde3. I have been using it for the last couple of days on my laptop and it has worked flawlessly. They can be found here.
http://cardinal.lizella.net/~vbatts/...ist/kde-4.1.0/
As far as upgrading to current, I haven't ever tried it, so I wouldn't know where to start for that, but plenty of people here do it, so someone will probably jump in here and give you that info.