There are several different ways you can go at this.  You can write a module for the task specifically, you can simply write an aspx page and then load it into an IFrame, probably some others.  The method you would use depends on you background and if you are comfortable with ASP .net 2.0 web pages.  The IFrame method allows you to write the page like you would any other page with database commands and code behind.  The Module method is dependant on you being comfortable with building modules.   Either method works well, I have used both depending on the project and what needed to be done.  My first was a standard web page with form in ASP .NET 2.0.  The second I did used a completely new module and the last combined a little of both. 

Jason,

One of the easiest (although not the most elegant) would be to use the DNN "User Defined Table" module (refered to as UDT for short).  It's one of the included modules. 

It lets you define a table and columns of various types.  A data entry form is then displayed that lets you add and maintain the data in the table.  You can find more information on this module here...

http://www.dotnetnuke.com/DotNetNukeProjects/ModuleUserDefinedTable/Downloads/tabid/878/Default.aspx

If you want to get into actual module development (coding in VB.Net) Michael Washington has an excellent tutorial here...

http://dotnetnuke.adefwebserver.com/DotNetNuke/tabid/195/Default.aspx

I hope this helps,

Chuck