Yes, you could either do a single node cluster, but you would not have failover capabilities.
http://technet.microsoft.com/en-us/magazine/2007.03.sqlclusters.aspx
or you could use virtual servers to do more than one node.
A lot of admins create a single node SQL cluster for every stand alone server they build so that if they decide to have a failover cluster in the future, they just need to add a node and it doesn't require a rebuild.