I would also ask you to bear in mind that although partitioning can work if one or more of the file groups is offline, this relies on partition elimination at compile time or run time - and the behaviour is a side-effect, not documented, not guaranteed, and liable to change with the next hot fix or service pack :w00t:
Partitioning in 2005 is almost never about performance in 2005. 2008 changes the balance somewhat - a white paper is pending on this. We will see.