I own a website build in .net and I want to make simple changes, including pictures, headlines and nav bars, from time to time. What software do I need. I have used Contribute (CS) on other sites (.php) I am involved with and it provides a visual reference while making changes. However, when I change the text on my site in CS I am sucessfull, but limited in what I can do and it doesn't provide the visual representation I would like while in the tool. Would like to find a new tool without having to learn code.

You can try Visual Studio by Microsoft. They have the 2008 beta out right now so you can use it free for the meantime.

Just an advice, if you frequently want to do cosmetic changes on your website, its good to have a CMS based site so that you can control the entire site from Admin Panel. SO you dont have to worry about any Tool.
For now you can use Adobe Dreamweaver CS3 which will server your purpose without worrying about learning code.

I agree with both bits of advice. I would just like to add that you can download Visual Web Developer from Microsoft for free. If you're just looking to make simple changes in a WYSIWYG type fashion, it should fit the bill.