To save a midi sequence you created in the Acid piano roll, go to the Track Properties of the midi track. At the upper right you'll see an icon of a floppy disc with a "?" in it for Save As. This allows you to save the sequence as a midi file. After you save it you can import it into any application that can open midi files.
To load a VSTi go to the Mixer field and click on Insert Soft Synth then click on VSTi Preferences. From there you can enter the folder(s) that contain your VSTi's. Then you can choose a soft synth by left clicking on the little piano key icon on the midi track.
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