>I have two Windows forms built with base classes. What would be the easiest way to adjust most of those classes with our custom classes?<

Start off with the custom classes to begin with? <g>

Seriously, though, for others who might be lurking, you can always sub-class everything to begin with (as I have been saying many, many times) even though you may have no code to begin with initially (it can be added later). Use these custom sub-classes from the beginning, even with minimal or no code in them, and you won't have to switch later.

Anyway, that doesn't help you now. The way I'd adjust everything is to go in to the code and simply replace all occurences of System.Windows.Forms.TextBox with MyClasses.MyTextBox, etc. ... and some things still may need additional tweaking, but hey, it's only two forms. It's not elegant, but it'll get the job done.

~~Bonnie