He is me in that case - thanks for the feedback, I'll try to remember to include both C# and VB examples in future posts.
You should be able to use a random function to choose your data, no problem. In the grid example from the blog post, you could use a random number to select a row rather than looping through them. For a combobox, you could use a random number to select by index. The easy way to get started is by recording a test that chooses a specific choice. Then right-click on the test step and choose "Customize step in code." For a Telerik RADcontrols for ASP.NET combobox for example (from your other questions, I believe you're working with a web app rather than Silverlight), you'd get something like this
you'd then just want to change the index (3) to your random value.
If you're not using Telerik controls, just straight-up HTML <select><option=...>, then you'll likely get a call to SelectByValue(). You can change that to SelectByIndex, again using your randomly-generated number.
Random random =
Then you'll need to determine how to best verify the results of a randomly-generated selection, of course - if you don't know what the inputs will be then how will the test be able to know what to expect; that may be the more difficult part but relies on what exactly your app does and what you're looking to test.