SQL 2000 cluster in-place upgrade to SQL 2005

I have a 2 node (Active/Passive) SQL cluster running on 2 2003 nodes. I want
to upgrade this cluster to a SQL 2005 cluster. I know that I can do a side
by side migration and install a new instance of SQL cluster and then migrate
the DATA - but I would rather not do that. I would rather do an in-place
upgrade

So I put the SQL 2005 Enterprise DVD in and started the install - it ran the
advisor wizard - said everything was fine. I had to choose which Instance to
install - I currently have the named instance DATA as my SQL cluster
instance - it did recognize that it was installed. I choose to install SQL
Database services - right underneath this checkwas was a checkbox that said
"Create a clustered service" - I assumed I should check this - so I did. A
few more screens - I put in passwords and then it asked me for Group names -
when I tried to put in my existing group names for Server, etc - it was a no
go.

It seems like the setup program should have recognized that I am already
running a clustered SQL service - should I have not checked that checkbox
about Create new cluster? It seems like it wasn't going to upgrade the
existing cluster, just create a new one.

when I went back and unchecked that checkbox about create a clustered
service - none of those screens came up - but it just seemed like it was
going to create just a regular SQL instance - with the same name DATA as my
cluster.

So I backed out of the install - everything is still working fine - it
didn't touch my SQL 2000 cluster. Any advice about when I go to the do
install the next time? Should I be checking that box or not? Do I have to
create a new instance name? or can I just keep the current one?