Android : Can I Get Proper Uri Of A Particular Contact In Droid 2.1?

I have written an application and added 2 contacts on emulator, but i
am not able to update their names on android 2.1, code is working on
android 1.6 platform with the following code.

ContentValues contactValues = new ContentValues();
contactValues.put(Contacts.People.NAME, firstName+" "+lastName);
getContentResolver().update(UpdateContactUri, contactValues, null,
null);

In android 1.6 i am getting Uri for those two contacts are "content://
contacts/people/1" and "content://contacts/people/2".

but in 2.1 I am getting these values are "content://contacts/people/8"
and "content://contacts/people/9" and while updating its giving
"java.IllegalArgumentException, Empty values" exception.

When i tried to put a static Uri like "content://contacts/people/1",
code was debugged sucessfully but contact was not updated.

How can i resolve it, why i am not getting uri like 1.6 platform ?