Sandy - If you use a mac those would be good options I guess, I am not familiar with Mac's, maybe someone with more experience can come along on that one.
Noah's wife - Are you using Windows or MAC? If you are on windows then using the notepad method above is what you could due to avoid having to keep putting the code into editors.
When you have the code you want to use, save the text document by saving as. Name it name.html (name being whatever you have chosen) and before you save change the drop down box with text to all files - then save.
Once you do this you can have it open as a web page in your browser and also as a text document by opening thru Notepad. Whatever is on notepad is what you will see in your browser, when you make changes to the html document save - then go to your web preview and refresh. It will show any changes you had just saved.
Doing it this way does not change the code at all. Then when you are ready to paste into Auctiva, use the text editor and save it - DO NOT GO TO PREVIEW IT THROUGH AUCTIVA. That is where it is screwing up. It should be how you want it by this point so previewing again isn't necessary.
Try this and let me know how you do.