i want transparent windows (for example a transparent console) !!!
Add Dibble's repo to your pacman.conf, update pacman, and download xcompmgr-cvs and transset-cvs. Open a terminal and use the transset command to set the desired transparency values for whatever windows you wish. Then run xcompmgr with the options you want.
(Don't use drop-shadowing unless you have a nVidia card, with renderaccel enabled. Otherwise, drop-shadows will make your GUI really, really slow!)