what shud b your minimum and maximum rank to be qualified for seven old iit's....???

Well it totally depends on what would be the Cut Offs for the year as then it would become more clear.

Askiitians provide the IIT JEE cut off along with the opening and closing ran given below for IIT JEE cut off:

http://www.askiitians.com/iit-jee-2011-counselling.html

Click for opening and closing ranks:  http://www.askiitians.com/iits-2009-2010-opening-and-closing-rank.aspx

Thanks and All the Best