n00b design suggestions: dynamic search criteria

Question

As a Silverlight learning exercise I'm trying to design a word look-up application. I'm modeling it after an existing word study tool called Zyzzyva (http://www.zyzzyva.net). I would like to implement dynamic search criteria, similar to the screen shot I provided below.

Basically I want to implement a combo box which contains a list of different types of search criteria (e.g. Pattern Match, Takes a Suffix, Length, etc). Depending on which criterion you choose, to the immediate right of that combo box, a related sub-criterion group of controls would appear.

For example, referring to the screen shot below..

When 'Pattern Match' is selected, to the right of the criteria combobox I want to display a Textbox to enter the search pattern.
When 'Length' is selected, to the right of the criteria combobox I want to display Min and Max number selectors.
etc.

 

What I am looking for is design suggestions on the best way of going about this. I have a web developer background and if I was to do this with ASP.NET I would probably make a web user control for each type of sub-criterion and then programmatically load the appropriate sub-criterion control on postback, based on the main criterion selection.

Is that the approach I should take with Silverlight? Or is there a more elegant / practical approach I should take. I welcome any suggestions.

Regards

Kevin Turner