what will happen if we change the mac address of suppose 3 of hosts in a lan and make it same..i mean i will assign same make address to multiple hosts in my local network..then what changes(errors) the network will see???

For starters it will confuse the switch as switches identify each pc by their MAC address, they store these address in a table in memory and hence is why each pc has to have a unique MAC address. I don't know exactly what will happen, maybe the data will be broadcast to every pc with the same address essentially turning the switch into a partial hub. It is a totally unnecessary thing to do.. As for ip assingment by the DHCP server that shouldn't affect anything as the the DHCP client on the pc requests an ip from the DHCP server on the router, so it is MAC address independent as far as know...

okk forget abt switches...consider a hub is there..now a frame will be broadcasted...so will all host which have the same mac address will be receiving the frame destined to dat particular mac address?? dats another thing, the packets will be discarded at ip layer,coz each host will have a distinct ip address..plz elaborate

What are you actually trying to achieve here?

i mean what effect will i see aftr i do dis?? in case of same ip address, windows machine shows an ip address conflict...so wat abt same mac address assignment?? will the system show any error or the NIC will just allow to pass the frame to network layer??

I think it will work like a hub if you have the same MAC address, but you may see some instabiity now and again.