plz tell me in detail how to download cui file 

[QUOTE=hemasanjeev]plz tell me in detail how to download cui file 
[/QUOTE]
From where? just as any other file .

Do you know what a cui file is?  Are you trying to load it in Autocad?  What version of Autocad are you using?  If you are trying to load the cui file into Autocad place the cui file in the support directory, then at your command line type in cuiload and browse for the file and then click on load.  You can load multiple cui files as well as mnu files.