in IIMs...i heard that only those ppl r placed who hav graduated from IITs NITs or other brand colleges....is it really so???

Whosoever has given you this information about IIM's has very minimal amount of knowledege coz it is nowhere close to even come true as it has nothing to with the functioning of IIM's. It does not matter if you belong to IIT's or NIT as it is totally dependent on the person and his/her ability to perform.