hi Vijay,
well.. if you forgot the local admin password you can reset it by using a boot able cd like Bart_PE, or Windows_PE there are many out there. But If it is for the domain admin then your in a pickle. as you have the option of trying to crack the hash which could take 10mins to 10000 years.. you should make sure that you have renamed the default administrator account to a different name and have a backup admin account just in case you forget the administrator password or the administrator account gets compromised
Cheers !!