Yeah. U wud be learning many new things in 11th and 12th. So how u did in the past doesnt matter much. U need to work smart more than work hard.
And yes, preparation for iit is very much sufficient for aieee. I prepared for iit, wrote the exam real horribly, ended up with a rank of 5142, as expected. Durin aieee, i kept my cool and got an AIR of 1100 for 220 marks.
I started workin properly only some 4 months b4 iit. I was very slack in my approach b4 that. I m trying again hard for jee 09.