Land Sale- Reg

Hi all Pls solve this Case! 

M/s XYZ P (ltd) has sold some acres of Land that was purchased some 15 years before. Now the sale was done in FY 2005-06. But the Company By Omission did not disclose/account  this ( Either in the Books nor in the Return of Income).

Now they want to disclose/account this now and pay LTCG tax on this.What are the Ramifiactions on the taxation side. Also tell me how to account this books in FY 2008-09. Whether this is a Prior period item or not?

Urgent Pls Guide!

Thanks