Thanks. It clears up quite a bit :)
It's quite confusing to figure out where to go, and what books and such are in print, and what system does what (Classic BT, alpha strike, and battleforce), but after your answer and reading Sartris's post on where to go next after the intro-box set, I think I got it mostly figured out...
Just, one last question… The newest box I got is the "25th anniversary battletech box set"... now is there any reason I should get the newer "BattleTech: A Game of Armored Combat", or should I go right for the Total Warfare books and so on instead? I intend to play regular battletech, and maybe at a later point look into Alpha Strike.