I wanted to know if my character is affected by a spell buff. Does she counts as dual natured for the porpose of being tragetted with mana spells from astral space?
No.
Only Dual Natured critters, (and characters made from natured critters - like Ghouls and Vamps) can be targeted from the Astral.
The SPELL itself, however can be targeted for the purpose of counter spelling.
an an adept with weapon focus be the victim of an astraly projected mage
No. It is the weapon focus that is dual natured, not the bonded owner. The Weapon Focus, like any foci, can be targeted for attack (disruption, disenchantment). but not the owner.
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What you are referring to was known as "grounding". This was where an astral construct could be targeted from the astral with a physical spell. (there is even an example of someone nuking a watcher spirit to take out the physical forms near it in one of the books).
This little trick was completely removed from the game in 4e, and continues to be gone. They have even gone so far as to re-enforce this with the whole "Separation of Astral and physical" write up in the book (but could have been better worded perhaps).