[XeTeX] Charis SIL font problems in XeLaTeX

[Bernd]

Hi there,
I just figured out why my bibliography looks diffeerent since I changed 
the font to Charis SIL, the \em doesn't work and I get this output:

> 
> LaTeX Font Warning: Encoding `OT1' has changed to `U' for symbol font
> (Font)              `operators' in the math version `normal' on input line 18.
> 
> 
> LaTeX Font Warning: Encoding `OT1' has changed to `U' for symbol font
> (Font)              `operators' in the math version `bold' on input line 18.
> 
> (./annotated_bibliography2.bbl
> 
> LaTeX Font Warning: Font shape `U/CharisSIL/bx/n' undefined
> (Font)              using `U/CharisSIL/m/n' instead on input line 1.
> 
> 
> LaTeX Font Warning: Font shape `U/CharisSIL/m/it' undefined
> (Font)              using `U/CharisSIL/m/n' instead on input line 4.
> 
> 
> Overfull \vbox (2.35547pt too high) has occurred while \output is active
> [1]
> Overfull \vbox (2.35547pt too high) has occurred while \output is active
> [2]
> Overfull \vbox (2.35547pt too high) has occurred while \output is active
> [3]
> Overfull \vbox (2.35547pt too high) has occurred while \output is active
> [4]
> Overfull \vbox (2.35547pt too high) has occurred while \output is active
> [5]
> Overfull \vbox (2.35547pt too high) has occurred while \output is active
> [6]
> Overfull \vbox (2.35547pt too high) has occurred while \output is active
> [7]
> Overfull \vbox (2.35547pt too high) has occurred while \output is active
> [8])
> Overfull \vbox (2.35547pt too high) has occurred while \output is active
> [9] (./annotated_bibliography2.aux)
> 
> LaTeX Font Warning: Some font shapes were not available, defaults substituted.
> 
>  )
> (see the transcript file for additional information)
> Output written on annotated_bibliography2.pdf (9 pages).
> Transcript written on annotated_bibliography2.log.


To me it looks like XeLaTeX can't access the italics? How can I change 
that? The Gentium font works fine, though, no problems whatsoever.

BTW, speaking of bibliographies, nobody has a real MLA bst file at hand? 
Those you find on Google are not really up to the task...

Thank you, Bernd.