what is the best encrypton ?

Does anyone know wat is the best wa to encrypt a file and send over a network to someone else which is best supported by VB.NET.And does anyone know how i can convert my string to bytes or ACSII .......................willing to hear from anyone suggestions

For converting strings to byte arrays you can use the System.Text.ASCIIEncoding class's GetBytes method. Have a look at this thread

There are several encryption methods supported by the framework.
The Rijndael algorithm is considered very secure. Have a look at the System.Security.Cryptography Namespace, and the RijndaelManaged Class in particular. I haven't tried it yet, so I can't give an example, but I am sure there must be some samples around on the internet.