Seriously, how many times have people started threads and said this?
You press the print screen button on the top right side of your keyboard,
-then open up your preferred software (MSPaint works just fine),
-right click and click paste - then save file
-upload to a photo hosting website such as tinypic,
-once uploaded, several codes will be provided, choose the one for forums and message boards, copy that, and paste it into your post - done.
The whole process will take less than 5 minutes if you're connection isn't dial up.
On trs2006 onwards, pressing print screen will automatically save your screenshot to the trainz folder in program files.