I'm having some trouble with dependencies it seems, but myself don't really know how to resolve the issue. Here's the output:

~:) sudo apt-get install build-essential
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.

Since you only requested a single operation it is extremely likely that
the package is simply not installable and a bug report against
that package should be filed.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
  build-essential: Depends: g++ (>= 4:4.3.1) but 4:4.2.3-1ubuntu6 is to be installed
E: Broken packages
~:) sudo apt-get install g++
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.

Since you only requested a single operation it is extremely likely that
the package is simply not installable and a bug report against
that package should be filed.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
  g++: Depends: cpp (>= 4:4.3.1-1ubuntu2) but 4:4.2.3-1ubuntu6 is to be installed
       Depends: gcc (>= 4:4.3.1-1ubuntu2) but 4:4.2.3-1ubuntu6 is to be installed
       Depends: g++-4.3 (>= 4.3.1-1) but it is not going to be installed
       Depends: gcc-4.3 (>= 4.3.1-1) but it is not installable
E: Broken packages
~:)

Edit: I just tried aptitude instead of apt-get, as suggested. Doesn't work, had other problems:

~:) sudo aptitude install build-essential
[sudo] password for ehsanul: 
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Reading extended state information      
Initializing package states... Done
Building tag database... Done      
The following packages are BROKEN:
  g++ g++-4.3 libstdc++6-4.3-dev 
The following packages have been automatically kept back:
  dpkg-dev fakeroot libdns35 libisc35 linux-libc-dev patch 
The following NEW packages will be automatically installed:
  libgmp3c2 libmpfr1ldbl 
The following packages have been kept back:
  adobe-flashplugin bind9-host dnsutils gvfs gvfs-backends gvfs-fuse 
  libatm1 libbind9-30 libgvfscommon0 libisccc30 libisccfg30 liblwres30 
  libnautilus-extension1 linux-headers-2.6.24-24 
  linux-headers-2.6.24-24-generic linux-image-2.6.24-24-generic nautilus 
  nautilus-data 
The following NEW packages will be installed:
  libgmp3c2 libmpfr1ldbl 
The following packages will be upgraded:
  build-essential 
The following partially installed packages will be configured:
  timidity 
2 packages upgraded, 4 newly installed, 0 to remove and 24 not upgraded.
Need to get 775kB/6265kB of archives. After unpacking 20.3MB will be used.
The following packages have unmet dependencies:
  libstdc++6-4.3-dev: Depends: gcc-4.3-base (= 4.3.2-1ubuntu11) which is a virtual package.
                      Depends: libstdc++6 (>= 4.3.2-1ubuntu11) but 4.2.4-1ubuntu4 is installed.
  g++-4.3: Depends: gcc-4.3-base (= 4.3.2-1ubuntu11) which is a virtual package.
           Depends: gcc-4.3 (= 4.3.2-1ubuntu11) which is a virtual package.
           Depends: libc6 (>= 2.8~20080505) but 2.7-10ubuntu4 is installed.
  g++: Depends: cpp (>= 4:4.3.1-1ubuntu2) but 4:4.2.3-1ubuntu6 is installed.
       Depends: gcc (>= 4:4.3.1-1ubuntu2) but 4:4.2.3-1ubuntu6 is installed.
       Depends: gcc-4.3 (>= 4.3.1-1) which is a virtual package.
Resolving dependencies...
The following actions will resolve these dependencies:

Keep the following packages at their current version:
build-essential [11.3ubuntu1 (hardy, now)]
g++ [4:4.2.3-1ubuntu6 (hardy-updates, now)]
g++-4.3 [Not Installed]
libstdc++6-4.3-dev [Not Installed]

Score is -9852

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