I started with Space Hulk and got sucked into Warhammer 40,000: Rogue Trooper (1987). Warhammer Fantasy Battles had already been out for several editions at that point. I only started getting involved with the 4th edition of WHFB (1992). This is the edition when they started with the army list books. 40K had a bunch of separate rulebooks - the Chaos books (which I never did get), the Ork books (which I did). Then they consoladated these into the 2nd edition rules (1993) and came out with the codex.
I did get most of those codices but when they cranked out the 3rd edition (1998) I only got the rules as a ‘placeholder set’. That is the basic rules to keep up with changes but not getting all the codices to fully keep up with it. When the 4th edition came out in 2004, I got a boxed set for my son but didn’t get the rules for me until recently.
Now that the 5th edition came out (2008) I am looking at trying to keep up with the codices – so far there have only been four – Space Marines, Imperial Guard, Space Wolves, and Tyranids. These are also some of the main ones I am interested in – I may delay picking up the Blood/Dark Angels. The others that I am keen on (and have figs for) would be Orks but I do have a bit of interest in Sisters of Battle and Necrons – both of whom haven’t had a new codex since 3rd edition. Army-wise, I could probably still field a Space Marine army and a passable Tyranid army – heavy on the Genestealers. I have a lot of Imperial Guard, Marines, Orks, and Eldar but not a lot in the way of vehicles for any of them.
In Warhammer, I did get all the 4th edition (1992) army books as well as most of the 5th edition set when they cranked that out in 1996 as there wasn’t a lot of overlap. When they churned out the 6th edition in 2000, I didn’t even get a placeholder copy. With rumors of an 8th edition to come out this year (2010), I figured I should get a copy of the 7th edition (2006) boxed set before it disappeared as it came with Goblins and Dwarfs – both of which I could use to fill out my armies. I can field an Undead army – which would now have to be a Vampire Counts army. I have enough figs for armies of Dwarfs, Empire, Bretonians, Orcs and Goblins, and a passable Lizardmen army but would need to paint all of them in order to field.
Depending on which way the rules slant, the 8th edition may be another placeholder set as well. Especially if I start trying to catch up on my 40K armies. Since they seem to be churning out a new WHFB set every 4 years - I can probably wait for the next one. Unles the boxed set has some cool figures. We will have to see.