Jerrick,
Geoff's answer is dead on!
The only other thing to consider is that there can only be ONE default
instance PER CLUSTER.
The second instance you install will likely be a NAMED INSTANCE.
The virtual server name you choose for your second instance MUST BE UNIQUE,
and the instance name will of course need to be unique as well.
Here are some good resources:

http://www.microsoft.com/technet/pro.../failclus.mspx
and in BOL -
Multiple Instances of SQL Server
Failover Clustering Example - This is very good and I think speaks to your
question perfectly as well.

Hope that helps!
Donna Lambert
Microsoft PSS
SQL Server Support