If they are not already installed, get the packages for gtk-engines (several included) and the murrine engine from your respective repository, although other engines may also be needed depending on which theme from Gnome-look.org or Xfce-look.org you want to install, but the above seem the most common.
If you have both desktop environments installed like me then following on from my last article you can just pick one of the styles and icons we added in Xfce under 'Preferences' --> 'Customise Look and Feel'. For example, if you previously added the Mint-X-Metal-Dark theme to your installation under /.themes in the users Home directory, or system wide in /usr/share/themes, you would be able to choose it in the Widget tab. Same goes for icons, where for the sake of this example I picked the Minty-Fresh ones. Then adjust Openbox's window borders to match the color of your new desktop and possibly also the mouse cursor and you're done.
That's really all there is to it. Btw, I've chosen this theme because it offers full transparency on the panel instead of the 'grey/white plate' that the stock ones leave behind for open applications. Have a look at the other post for links and a few other themes. All that remains is to find a more appropriate menu button for your installation instead of the ugly default monitor graphic, and maybe adjust other applications like Gkrellm to fit in. This one is an exceptional choice for getting rid of panels and applets altogether. The Gkrellm plugins package can be found in most repositories, if not there then here is a link to the home page, together with a guide to this extensible system monitor. A good choice on other minimal window managers like Afterstep or FVWM instead of dock launchers and applets, and with the launcher, volume and systray plugins among others also a full replacement for a panel.
So overall, if a Mintified LXDE is what you wish for, the result could look something like this:
|Mint-Metallic menu, greenz Openbox theme, OSX_Aluminium icons|
|LXDE with Noir Crystal icons and Wbar, top panel auto-hiding|
Well, this entire post just seems like an excuse for me to upload a few more screenshots, but I hope you enjoyed it and learned a tiny bit, possibly, or at least got inspired.
P.S. Overall I find options limited in LXDE, but a nice wallpaper will go a long way.
Edit: Added the Iceberg screenshot.