iTunes problems.

[RgrsMario]

I got iTunes on a Acer Aspire 5730 with WinVista on it

i got 2 problems i need help on

1. Sync confusion

i got a iPhone 3GS and every time, and yes i mean every time, iTunes will erase 169 songs from my iPhone and "update" it with those same songs, or it'll randomize it each time with different artists. How the hell do i stop that ?

2. Previews

Each time i wanna preview a song or even a movie, iTunes will crash.
i dunno if its within itunes, or a codec problem

Any idea ?

[reactive]

Make sure you have the most recent version of iTunes

Uninstall iTunes and reinstall it.

Try a different USB port (syncing issue)

I'm not sure about the format of your movies, but you shouldn't need any codecs to listen to your music. Sounds like a screwy installation of iTunes.