Dotnet custom interface

Hi everyone I'm trying to build some custom controls in dotnet using struct (base on a LoneRobot project: http://lonerobot.net/?p=267

I'm relatively new to dotnet (less than a month) so there still many things I don't know or understand...

So far I have make some UI controls: buttons, checkbutton, and custom panel that can be clicked to change their size (dropdownpanel).

I tried my best to understand the most I could, but now i'm struggling a bit... For those who wants, I joined two ms files, the struct files and a test file to see the code in action

First issue, when I add icons to my checkbutton, the alpha blending is monstruous (check the alpha_issue.png) and I realy don't understand why... I try to change the interpolation mode but it didn't change anything....

Second issue, well that's more a general problem than a specific one. The thing is a don't know many aspects of dotnet yet, so when I want to do something, I often use some ugly tricks to do it, while I'm sure there would be a better method to achieve the same result (or a better one...).
So for those who are actually a bit motivated to help me on on improving the general code, I would be very glad :)