I thought I read on the MTR you have to be on at least SP17 or SP21 (I don't remember which off the top of my head). We are on SP21 and will be upgrading to V5R2 in two weeks.
tgore is right. With V5R2, you have to be at least on SP21. For one of my clients, we have upgarded AS in V5R2 and Xe in SP22 OneOff H1 ... the last OneOff enable on KnowledgeGarden is not yet very stable.
Be careful too, there's a lot of PTF necessary.