Paint.NET :: How To Set Save Default Format To BMP

I'm new to Paint.net.

Until recently, I was using the paint app of Windows 7. However, the office changed my laptop to a PC running Windows XP SP3.

I do a lot of documentation work and part of my job requires me to save screenshots for posterior use in product manuals.

My situation is this:

I have to save in .bmp format (office policy) and, by default, Paint.net saves in .png format.

Is there any way to set the Save default format to .bmp or any other format?

Secondly, when I save a file that contains a period in its name (for example "ch2.p16" - chapter 2, page 16), it will save the file but not in the format selected. Instead, Paint.net assumes that anything after the period is the file extension. Thus, the file is saved as "ch2.p16" with a file type of "p16".

Is there any way to bypass this glitch other than having to avoid using periods in the file name? (I've attached an image)