Welcome to the board and Pentax in general! I too have a K100D Super that is my first DSLR. For post processing I think keeping in mind your experience and type of shots I would download Picasa and give that a try. It is a small quick program to help you make general tweaks to correct small things with your photos. For more advanced processing I use Lightzone (
LightZone : Advanced photo editing made simple) and find it intuitive and easy to use.
Now on the subject of batteries. If you do a search you will find a ton of threads on the subject. However here are the rechargables that I find work best for me:
1. Sanyo Eneloops - Hybrid low discharge batteries. I have 12 AA and 8 AAA versions. I used these in almost anything in my house that needs batteries
2. Ray-O-Vac Hybrids - Again low discharge hybridge recharagble batteries. I have 4 that I bought at a Target while on vaction when my first set of Eneloops died.
Welcome and good shooting!