I was thinking about install kde 3.4 on my laptop(Inspiron 8600, Slackware 10.1 + kernel 2.6.10). How should I do it, from source? can I use /contrib/slackware/10.1 package with kernel 2.6? If so, how can I use the pkgtool to install? should I uninstall all other kde packages before, or just overwrite? How stable is kde 3.4 compared to 3.3.2? And last but not least, why should I update to kde 3.4 at all?

Greetings
siggiae

KDE 3.4 is now in slackware-current.
Just use some automatic slackware update tool. Or download the packages directly from a slackware repository, and run upgradepkg for them. There are tools to help you with that.

KDE 3.4, in my experience, is just as stable than 3.3.2, but it has definitely a number of bugs. That's perfectly normal as it's a new release, and 3.3.2, as its name shows, has benefited from two revisions. Wait for 3.4.1 if you want, it will probably correct these bugs.

to upgrade packages, don't do
removepkg+installpkg,

do
upgradepkg

You'll find a list of new 3.4 features on www.kde.org. But no one asks you to upgrade, there's no hurry.

of course you can use packages from /contrib/slackware/10.1 with your 2.6 kernel.

KDE 3.4 has been great for me.

Its been generally stable for me. I am using the Slackware current packages as well.