SX3 should support DXI, I find its what most FX plug-ins use, it is the new version, Cubase 4 that does not support DXI and wrappers have to be applied, or so I have heard as I have not upgraded to version 4 for that very reason, people say the wrappers are easy to use but my Cubase runs perfect on my system so I find no real need to get 4 other than I would like to own it. Anyhow from what I have heard the wrappers, (if that is in fact what you need), can be purchased at Guitar center or any online music shop that carries them, guitar center or any other walk in shop that sells it would probably be better as the staff at some of these places can point you in the right direction and alot of them that work in pro audio departments have studio's and can help, sometimes. I have heard you can buy wrapper programs for about $60.00 but I'm sure price varies.

My other question would be, when you install the smartflute are you looking for it on your VST list, or are you looking for it in your FX plug-ins section? Chances are it did install but it is either only available as an FX plug-in, also it may be on your FX plug-ins list and may not be called smartflute, it could say Music Lab with a side drop out that when highlighted might say smartflute.

All that said if you are trying to install as a VST and it is not showing on the VST equitment list then it may not be compatable with Cubase SX3, if it is a cracked program it could just not be a good copy, sometimes cracked stuff will run a little pesky.