Oracle question from a SQL Server DBA

I am an experienced SQL Server DBA starting to learn Oracle. I am comparing the two systems and would like comments on the following points.

Table update locks:
With SQL Server, if I run a query that updates every row in a table the entire table will be locked. If I simaultaneouly run a select query against the table the query will hold until the update either commits or rolls back. If I do the same in Oracle, the select query will return the old snapshot of the table ( from rollback segments) before the update is committed. The user is unaware of the fact someone else is updating the table and the Select results will be out of date as soon as the other update commits. The SQL Server user will know someone is running an update (due to the hourglass) and will try again later. He is always sure that any Select results he obtains are committed ones.
What are the pros and cons of these methods?

Cold sever backups:
With Sql Server, I can copy *.DAT in MSSQL\DATA to another machine with SQL Server loaded and everything will be up instantly. All database configuration are stored in Master.dat.
Can I do the same with Oracle? Would I have to re-create the database instances in the Registry? Please comment.

Integrate Login:
Can I authenticate an Oracle user with the NT login?

Performance monitoring:
Where can I get Oracle counters for perfomance monitor? SQL Server has a whole bunch of them and that facilitates tuning a great deal. Received on Mon Mar 02 1998 - 00:00:00 CST