Hi Elizabeth, welcome to the forum.
There are a couple different ways to accomplish this via InfoPath.
A great solution is the Database Accelerator for InfoPath http://www.qdabra.com/proddetail.asp?prod=QDBXL1
This was designed with your situation in mind, where you want to have a great form which ties into a database and provides a real enterprise solution but you do not want to have to learn about webservices and invest in learnign all the backend setups. With DBXL installed on your database server you get a whole suite of webservices which you can start using immediately to submit your form. This also gives your form additional features, such as access control and permissions. In your example you could set it up so that employees can only submit or view their own time cards, and the ability for managers to only see their direct reports, etc.
We also have an InfoPath solution specifically for Project Management called project tracker. This is includes time sheets as well as Scope of Work Documents, etc. http://www.qdabra.com/services.aspx
Otherwise you would need to create your own webservices from scratch or create a new form from scratch that connects to your SQL server. Unfortunately, a form which submits to a database has to be designed as such from the beginning and an existing form can't be converted over to submit to a database.
You can email me directly if you need more information.