Can additional self assessment tax be paid after filing return?

In one case, self assessment tax was paid and ITR-1 form filled up and submitted electronically on 31st July, 2012. Later it was realized that some amount was forgotten while calculating income tax and extra self assessment tax is yet to be paid. Can this be done now? In this case, if the dept accepts the revised return. should the person send two ITR-V forms (the first one, though incorrect, should carry signature to validate the submission and the final one also for the same reason)? Thanks for suggestions.

If i am paying tax on every item I bye or consume, why should I pay additional income tax?

I am paying sale tax, road tax, entertainment tax etc then why is govt. forcing us to pay Toll tax, income tax etc. It is same as paying twice for same thing. Is it not the duty of govt. to make the roads, and bridges etc. And if govt is taking income tax from us then why should we pay various tax on every purchase or consumable we take.In the end of year a middle class man is left with nothing, only empty handed.

Income tax payment for additional incomes than salary?

I work in a IT company where Incxome tax is detucted in our salary. I have earning of 100000 from my investments. I had to pay an additional amount of 10000 or so as Income tax additionally to what my comapny detucts for income tax. How can I pay this. Do I need to show any documentation for my 100000 earning while paying this.
I got the money b investing the money in shares.