[Dock-fans] g++ installation

[anantha ramanan]

Dear All
               g++ is not installed in my system, i am trying to install it
by using following

"sudo aptitude install g++"

Its started  installing but  i am getting following problem

Please insert the disc labeled 'Ubuntu 7.10 _Gutsy Gibbon_ - Release i386
(20071016)' in the drive '/cdrom/' and press [Enter].

I dont have any cd, how can i install g++ in my system without the cd?
Anyone help me to install dock6 in ubuntu.

Regards

Anantha ramanan.R
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