If I understand you correctly, I believe what you wish to do can be done.
Firstly, did you take a look at BitLash as suggested by BillRoy, as it might be a good and suitable solution for you?
I have spent the past months learning and developing a system where by my Arduino monitors my renewable energy system and makes it availible for viewing on the web.
What I do, is have the Arduino use a http POST, to send data to my hosted site where a php script either stores the data in a SQL database or in a file.
You need to know what structure you wish to use to transfer the data, I use json format.
Data that I want to go back to the Arduino, I hide and I make it so this function is not available from the web-page normally, as in my case, it is not something I would normally want anybody to be able to do from the webpage. But you can make possible from the web page by using an authorisation system.
I am no expert, and still learning myself, with a lot of reading and trying things out and help from other clever programmers e.g. http://www.cs.helsinki.fi/u/ljlukkar/iot/
To have an idea, you could look at my devolpments in my signature.