Here is a great link to a Shonda Parker's blog, which has a great article about flu prevention and treatment. She is a very knowledgeable lady, who's advice can be trusted...
Shonda Pedia: Swine Flu Update
In addition to this great article, I'll mention a few things we are doing at our house:
Since it takes a day or two for the virus to make a home in our bodies, we do these things after we have been out around other people ...
1.) Swab out our noses with salt water on a cotton swab, or do a nasal wash with Xlear or our netti pot.
2.) Gargle with salt water or Listerine.
3.) Rinse our eyes with saline drops.
I have also heard that colloidal silver (be careful what you use is made by a reputable company and taken in proper doses) is knocking the swine flu out successfully and is also being used as a preventative treatment.