I know that but I already have the file . Do I have to install into the machine or just open Xterminal and so on ..? get confusion ..! if have to be install it's come up 2 choice like said above .. no clue ?[/QUOTE]

Extracted from the first post from Lacedaemon...

//== Theme Installation ==\\

1) To install you need to transfer the downloaded .deb file to your N900(for example Documents folder)
2) Open xterm and type(you need rootsh for this):
Code:
sudo gainroot
dpkg -i MyDocs/.documents/darksky.deb3) Close xterm, go to Desktop -> Desktop Menu -> Themes to change theme.

If the theme doesn't look as it should it is suggested to reboot your phone after the installation.

\\== Theme Installation ==//