Wanting to add a new desktop environment to my Slackware 12.2, so I'm thinking about trying KDE4.
But I don't want to remove KDE 3.5, what is the best way to go about this?

Thanks in advance

If you used the packages from official Slackware media, it isn't possible. You must choose one of them.

Thi8s sort of thing often can be done, but not, as has been said, with official packages.You would have to download the source code, and build it to reside in a different place. Some idea of the suffering involved can be gathered from

http://www.linuxfromscratch.org/blfs.../kde/core.html

Now linux from scratch uses different places for things often - /usr/X11R6/lib instead of /usr/lib/X11 for example. It uses patches that might throw the build because of this. No we will not babysit this. If you decide to have a go, I would suggest a long read of
./configure --help with each package, and then
./configure --prefix=/usr/local or somewhere other that /opt where kde normally resides. It is much simpler to remove and replace, and just spend 3 days tidying up after that. But you seem ready for suffering. Me - I stay with a low cholesterol window manager like xfce

If you really enjoy suffering, there's an unstable book for LFS as well, using later versions with instructions that might work.

It was possible to have KDE 3.5.x and 4 on your computer at the same time as 3.5.x installed in kde and 4.x into kde4. However, I think with the release of 4.1.3, you were no longer given that option. You might want to look around on the KDE site and see if you can find more information on the subject. However, KDE 4.2 is suppose to be released in a couple of weeks so it might, repeat, "might" be worth waiting.
Unless the applications for KDE 4.2 are as "improved" as the hype would have us believe 4.2 has been "improved," it won't be worth the wait.
Pushing this absolute piece of junk on the public when it was far from ready is reminiscent of microsoft and the biggest disservice to the end users I've seen in the 14 years I've been using Linux.

Thanks guys. I did some more searching and this post looks pretty helpful:
http://www.linuxquestions.org/questi...24#post3164824

If this doesn't work out, I may just put Slackware-Current on a spare partition and install KDE4