With Slackware 12 in Xfce everything seems to run fine, except Alt key
on keyboard. When I press the normal Alt+F2 - nothing happens. The
same for AltGr+F2. Action is performed only if I press both alts - Alt
+AltGr+F2, which is quite annoying.

I've asked for help on xfce forum, they requested me to make a new
keyboard shotcuts scheme. Result was: in Xfce settins manager I had
choosen window manager->keyboard->add. After this, the current
settings has been copied into new one. When I for example modify the
'Close window' shortcut to only 'F4' it works. Then I choose to bind
it back to Alt+F4, so I press only one (left) Alt and F4 and the
shortcut is created, the shorcut field states Alt+F4. But to use it I
still need to press both alts.

In KDE alt is working as expected. Anyone has any idea to help me with
this?

link to xfce thread about this topic:
http://forum.xfce.org/index.php?topic=3484.0

input secion of xorg.conf:
Section "InputDevice"
Identifier "Keyboard1"
Driver "kbd"
Option "XkbModel" "pc105"
Option "XkbLayout" "us,sk"
Option "XkbVariant" ",qwerty"
Option "XkbOptions" "grp:shifts_toggle,grp_led:scroll"
EndSection