Do you mean pg_admin or pg_dump, or is it pgAdmin tool you are enquiring about. If you would like to dump selected tables from either a script or from the shell, then with pg_dump you have a -t (--table) option which you can can use to specify the tables you would like to dump or alternatively -T (--exclude-table) to select the table you would like to exclude from a dump. Hope that helps.
I've just realized that I can't dump once all selected tables with pg_admin . is it true. ? I can't belive. Does anyone has this issue ? Of course I know I can dump the whole schema but that is not the matter.