First off you can do 2 node clustering with SQL Server 2005 Standard, which should make your boss happy with the budget.
Secondly, windows 2003 clustering in itself is a topic to learn - take this seperately.
Thirdly, in clustering you have many nodes, but one instance of SQL Server - don't confuse yourself thinking there are many SL Servers.
And fourthly, 2005 is cluster-aware, the installation will recognise the OS is clustered - you will need to supply a virtual SQL name and IP address.
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