Uploading to a website

How can I upload a file to a website using AppleScript?

I have the following code to find the file on my system:

set theFilePath to POSIX path of (choose file without invisibles)
set content of text field "fileToImport" of tab view item "importData-Tab" of tab view "tabView" of window "mainWindow" to theFilePath

Now I want to upload the file using POST to a website. Please Help!