Without a snippet for your time problem there's not much to say apart from speculate.
For your dbMoveSprite() problem, are you using 'float' variables instead of 'int'? Also the gravity can be solved just by decrementing the Y coord each frame by a certain value. You may have to do checks on the Y coord to make sure it doesn't go out of range, and collisions, etc.
Your MP3 problems I'm not sure, have you tried playing them from DBP and seeing if they work with that? Could be anything from a bitrate format not being compatible, not sure. Anyhow, if you are still needing them, then you could google the bass.dll which plays almost any music file. You will have to include the bass.dll in your executables directory but it does come with a header file which you can include in your source.
Mental arithmetic? Me? (That's for computers) I can't subtract a fart from a plate of beans!
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