You don't need any third-party software. Get the screen you want in BeerSmith, then press the Print Screen button on the keyboard. It's usually at the top-right, to the right of the F12 key. That will "copy" a shot of the screen. Then open Paint (comes with Windows, in the Accessories area of the Start menu). In Paint, click Edit->Paste. This will paste the entire screen contents.
Click the dotted-line square at the top of the toolbar column on the left, and drag a box around the bit you want to keep, then go to the Image menu and choose Crop. Then, save the image as a JPG file (or PNG if it's got text, it comes out clearer).
Once you've saved the image, upload it somewhere. Photobucket or http://imageshack.us
are good. Once it's uploaded, you can put a link to it in your post on here.