ENCODING loss on Read and Write file

[teo]

hallo
encoding loss here, i presume
situation:

Visual Web Developer 2005 creates a new html file

with Visual Web Developer 2005 I write some odd chars

the browser displays them good

now:

with vb code net (fx 2.0) I open the html file

I add the "hallo" string in the Body section
(near the odd chars)

I save the file

the browser doesn't display the odd chars
(now I see only the ? char in their positions,
that is the question mark)
QUESTION:

how to open and write a file
keeping the original encoding
(I think when managing html file
the encoding offered by Visual Web Developer
is the best and it is to be kept ) ?

Or at least, never loose an odd char after Reading and Writing?

Code, ideas, workarounds, external dll...
everything is appreciated