You missed an upgrade method particularly applicable to 2000 to 2008 (R2) conversions:

Machine swap.

You have Server, with SQL2000/5.

You buy/scrounge/spin up a VM NewServer.

You install SQL2008(R2) on NewServer.

You write down the IP's of each, then swap their IP's, swap the names, rejoin the domain if applicable, and change the SQL Server name.

Wait N days, then get rid of Server (old).