I want to set up a user account on my laptop to access the network of my office, and in order to do that i need to install applications using my office ubuntu repos, is it possible to create a sources list file to use only by 1 user account, and the rest to use the common sources?
You can have separated sources lists, but that only means than each repo you add will be defined in a sources.list file which makes more easy to purge a problematic repos. I did that using ubuntu-tweak (there's an option to store each repo in a separated file in the softwar origins tab). But I don't think you can have diferent sources for diferents accounts, since the sources are system-wide and not account specific.
Think about it, that would mean you would have diferent versions of the same program installed in the same system which would be a potential disaster. If an user install libreoffice 3 from the ubuntu repos but another install libreoffice 3.4 from the libreoffice external repos, the 3.4 would "smash" the 3 installation... not to talk about the potential dependency hell you will cause...
The only way I can think for having a diferent account with diferent repos is making a diferent partition in your laptop but that's having two diferents ubuntu installs in the same computer. Then you can use your "normal" ubuntu at home and your "workplace" ubuntu with the office repos. You can make the install so they share the same /home/user so you'll have the same configuration files, the same user, but diferent programs.
Other solution is to install a virtual ubuntu inside your normal ubuntu trough virtualbox, and link that virtual-ubuntu to your office repos. If your laptop is not much old it can handle a virtual os inside the main os without problems for normal office applications like office and such.
Wish it helps, good luck.
I believe only one user account is able to install software from any apt repository: root. You don't have to login as root, of course. You normally use sudo to direct the root user to perform these actions on your behalf, but it's still being run as root. Since only the root user can install software, it wouldn't make much sense to provide a sources.list per user. But if you want to separate the office repos from the other ones, then you might add the deb-line(s) in a new file and place it in /etc/apt/sources.list.d/.
Your question wasn't easy to understand, though, so perhaps I misunderstood?