Oracle upgrade on veritas cluster 5.1 SP1

Correct, install new binaires on both nodes and upgrade the database on one node.

For VCS, you will need to update anything that changes for the VCS Oracle and NetLsnr resources which is likely to be just "Home" attribute.  You may have to upgrade the agent itself if it does not support your new 11.2.0.3 version - you will need to check the agent doc for the version you have installed.

You should freeze the oracle service group while you are doing the upgrade.

I don't know of any docs for upgrading Oracle in VCS - I only found this in the UNIX agent guide, but the information is applicable to Windows too:

$ORACLE_HOME directory on local disks

You can install the Oracle Database Server

($ORACLE_HOME) on the local disk. The advantage
(over $ORACLE_HOME directory on shared disks) is that

you can upgrade the Oracle database binaries on an offline

node while the database server runs on another node. The

database server can later be switched to the upgraded node

(provided the database is compatible), permitting a minimum

amount of downtime.

The disadvantage of this approach is that with a large

number of nodes, it becomes difficult to maintain the various

Oracle installations.