Could I ask what kind of web server you are intending to use?
If you are using a standard web host that probably offers PHP and SQL then you will need to create you web-page in html, obtain the data from a form using PHP (or perl etc) and store it in an SQL database. Then use the ODBC driver to import data from your SQL database to your Filemaker database.
There are hosts out there that offer Filemaker servers so that you can run your database on their servers. There is one that is offering a $99 per year package at the moment for Filemaker Pro 10 databases. You collect your data from your webpage using PHP.
If you are made of money you maybe lucky enough to obtain a copy of Filemaker Server, but for the task you are trying to achieve this may not be very cost effective