And I'm using latest foo_ui_columns.dll ...

Cygoku

there are several versions and releases scattered around here, make sure that you have this one

You use them like a splitter in prefs -> columnsui-> (Layout tab)

Isn't this plugin use to put multiple left-sided panel such as Lyrics, Album Art etc,... ??

Cygoku

It makes tabs.
In those tabs you can place other columns panels or splitters.

In my config I use foo_uie_tabs to change between the things below the track_info_mod panel (i actually have the tabbar hidden, some of my older configs, it is visible))

If you want to use it for multiple left side panels, you sure can.

I remember last year, I had a friend with foorbar in wich his tabs were integrated into the left side of it's foobar instead of dockables window(s),...

Any idea ?!?!

Cygoku

no.
a picture is worth a thosand words.

You can put the tabs anywhere you want. If you want only one side of the window tabbed you can do something like this:

Horizontal Splitter
+ Tabbed panel stack mod
| + Album List Panel
| + Queue Manager
| + Track Info Mod
+ Single Column Playlist