I gotta answer....
S i did change the paramter Oracale_Sid in Registry...
Path is Go to registry....

My Comp>HKEY_LOCAL_MACHINE>SOFTWARE>ORACLE>HOME

well actually i have 2 versions of oracle running on my machine....
so i have hom0 and hom1.versions are 8.x and 9.x

In 9.x , in the path specified u dont have entry Oracle_SID, u have to create a string with name ORACLE_SID and enter the data(database name), in 8.x u have defualty the string, all u have to do is edit the data to change defualt database.

i dunno y 9.x dosent hav an entry as such....

Please if any body else who knows how to change default other than REGISTRY please let me know.....

AS stecal was telling a method to do so.....am not aware of it...please can any 1 explain it to me....


Regards
Abhay.