If you’re like me very fond of Thunderbird (or Firefox, Seamonkey, GQView, Pidgin and similar GTK applications), and are geek enough to run Slackware while being complete novice to Linux – you’ve probably noticed that your GTK look’n'feel is like..well complete crap.
To get rid of this issue, I used to install themes, or for applications other than Thunderbird just got used to their ugly look, but then yesterday I got Ubuntu 8.10 disc and my brother’s notebook. Combined, they demonstrated me one of the best out-of-box distributions, and you know what? GTK applications in there look really nice! That was a moment I realized that my Slackware shouldn’t be left behind (well, it took me only 2 months to figure that out – kudos!). The only thing that was required is to enable Xfce configuration:
$xfce-mcs-managerOnce typed into console, try to re-open one of your GTK2 applications – you should be amazed how ugly previous style was. If you don’t want to initialize Xfce manager manually on every login (and you don’t) you have to make sure that this command is invoked when your window manager launches. For me, I just put the xfce-mcs-manager command into .xsession file (depending on your configuration .xinitrc might also be an option).
Hope that saves you some time, and you’d be smarter than me 
If you need more similar tips – make sure you read How to properly setup Slackware Linux!
UPD: Checkout xfce-setting-show if you want to manipulate Xfce settings.
You can also install “gtk-chtheme”, which is a wonderful program that lets one set their gtk theme using gnome themes or whatever. That shouldn’t require a daemon running or anything.
I would try that, thanks for your suggestion!