Yes, it is a good idea to check the tutorials.
In general, the most important thing if you want to make VGA-backgrounds is however - to gain the skill of drawing. Even though you had the best graphic programs and tools, you can't make a good pictures if you aren't a good drawer.
I started my own game project about 1,5 years ago, and it took over year to learn how to make good enough backgrounds. Now, when I know how to make them it takes normally just an one day to make one background. Please check the thread "Background pictures" to see some of them. Instead of 320x200, I'm using 640x400 resolution but it doesn't mean that the game couldn't have a same kind of atmosphere as Sierra's games had.
Probably there is not just one simply way to make "Sierra-style backgrounds". Someones make such as backgrounds by altering original backgrounds from Sierra's games, but I personally don't like that technique. Like Blackthorne519 said, you must just practise drawing and ask opinions about your pictures.
Good luck.