Good questions...

1)Whats the diff between 10g enterprise manager and the 10g grid control ?

Same thing. I think they realized they went overboard with the "Grid" word and now they're starting to call it 10g EM.

2)Do i need to install anything on to the client or everything will work from the web browser (some DBA's are saying i need to install the java edition on my client i dont understand that)

Most features work from the browser. Some features work only from the Java client (like OLAP). There's a matrix out there somewhere with the features of each.

3)Can i use 10g enterprise manager to manage 9i databases ?

Indeed. You will need to install the 10g agent (to it's own $ORACLE_HOME) on the server the 9i database is running on.

4)I saw a option called as cloning in 10g enterprise manager can i use this option to clone oracle 9i databases ?

Yes. I believe it'll just create a job & rman script that'll do an rman db dup.

-Ken