Thanks for writing! The short answer to your question is that netbooks are usually below SmartMusic's system requirements both in processor speed and audio hardware that is able to play sound and record sound at the same time (aka full-duplex support). As such, unmodified netbooks will struggle to sucessfully run SmartMusic.
You can find more information about using SmartMusic on a netbook at this thread:
As you'll see, one of our users says he got good results when using an external sound card with the netbook. While we have not officially tested this scenario, we have had unofficial reports that this improves performance of SmartMusic on a netbook.
An example of an external sound card is the Griffin iMic adapter (designed for Macintosh machines, but works equally well on Windows comptuers with motherboard audio chipsets).
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