Dear All
thanks a lot for all your inputs..
@ russel
since i have around 500 activities i have to change the duration for all the activites and there are around 50 milestones with constraints.
so if i copy the first project and keep on changing the dates time it will take more time...which i wanted to avoid.
finally i got it done this way
since both the project are same only difference in time and duration.
first i exported both the projects to spreadsheet with the reosurces/budgeted units/time /activities column
then i copied the resources assignment form the first which has reosurces assigned and pasted in the 2nd project where i have to copy the resorces. then i copied the budgeted units/time also.
by this i got the resources assigned to the 2nd project with the same budgeted units/time.
then i imported the 2nd project to p6. i had got all the resources asigned to each and every activities without changing the time and duration.this took me just 5 minutes.
hope this is also a good option...