So I can't exactly find this PDF on Games-Workshop's site anymore (I think they've done away with their online articles), but it looks fun so I don't want it to be lost to the Warp!
The rules are as follows, as taken from:
http://www.games-workshop.com/MEDIA_CustomProductCatalog/m1150687a_Warhammer_40,000__The_Dividing_Line
THE DIVIDING LINE
All good generals have heard of the maxim ‘divide and conquer’, but what if the battlefield itself were split in two? In the war-torn future of the 41st Millennium there are all manner of force fields, Warp barriers and other bizarre phenomena that can effectively partition a battlefield right down the middle and separate the armies fighting across it from their own allies. Part of defeating your enemy is having the right forces in the right place at the right time. What will you do if the troops you need are stuck on the wrong side of this dividing line? Will you expend time and resources tearing down the barrier to bring your combined force to bear, or will your troops forge ahead on their own, trusting to their own fighting skills to overcome the odds?
THE ARMIES
Each player picks an army from a Warhammer 40,000 Codex army list, to an agreed points total.
THE BATTLEFIELD
When setting up the battlefield, place a series of suitable markers in 12" intervals in a line that bisects the gaming board across its width, as shown in the diagram. These markers represent Force Field Emitters (see special rules below). Set up any remaining terrain in a mutually agreeable manner.
DEPLOYMENT
The players roll off, and the winner chooses to deploy first or second. The player that goes first chooses one of the long table edges to be ‘his’ own table edge. The opposite table edge is his opponent’s table edge. Starting with the player that will deploy first after deciding table edges, but before deploying any unit each player selects a point in his own deployment zone to be an objective (by placing a counter on it or any other clear method). These objectives cannot be placed in impassible terrain or within 1" of the dividing ‘force field’ line. In addition, the two objectives have to be placed on opposing sides of the force barrier. The player that won the roll-off then deploys his force on the table anywhere up to 12" from his table edge, making sure that no unit is within 1" of the ‘force barrier’. His opponent then deploys his force in the same manner, from his table edge. Deploy any Infiltrators and make any Scout moves.
FIRST TURN
The player who deployed first gets the first turn. His opponent may attempt to Seize the Initiative by rolling a dice. If he does so, and the result is a 6, he will get the first turn instead.
GAME LENGTH
Roll a dice at the end of game turn 5. On a 1-2 the game ends immediately, and on a 3 or more the game continues. If the game continues then roll the D6 again at the end of the 6th game turn, and this time the game ends immediately on a roll of a 1-3, and continues for a 7th and final turn on a roll of 4+. The game ends automatically at the end of game turn 7.
VICTORY CONDITIONS
At the end of the game, the player controlling the most objectives wins. A player controls an objective if there is at least one of his scoring units, and no enemy unit (any unit, whether scoring or not), within 3" of it. As different objectives vary in shape and size, it is important to agree at the beginning of the game exactly where this distance will be measured from. If the players control the same number of objectives, the game is a tactical draw.
SPECIAL RULES
Force Field Emitters: The battlefield is bisected by a series of objects (void shield pylons, Chaos Warp emitters, psychic field relays and so on) that project an impenetrable force field between them. Whilst a Force Field Emitter is within 12" of a neighbouring emitter, there exists between the two an impenetrable force field. This force field blocks all movement (even skimmers and jump infantry), line of sight and shooting attacks (including barrage weapons). If a blast
weapon scatters across the force barrier reduce the scatter distance by the minimum distance so that no portion of the blast marker falls across the opposite side of the force barrier. If a unit deep strikes onto the battlefield but they scatter onto the opposite side of the force field barrier to their intended target, then they will automatically suffer a Deep Strike Mishap. Each Force Field Emitter has an Armour Value of 13 and 3 hull points. Each glancing or penetrating hit inflicted on a Force Field Emitter will cause it to lose a single hit point. If a Force Field Emitter is reduced to zero hit points it is destroyed and removed from play. As Force Field Emitters are destroyed, the force field will begin to weaken as follows:
• If a single Force Field Emitter has been destroyed, the force field between the two emitters to either side of the destroyed emitter starts to weaken. Units may move between this section of the force field but it counts as difficult terrain and they must take a Dangerous Terrain test. Units may also shoot between this section of the force field but they must first roll to see their target using the Night Fighting rules and their target will receive a 5+ invulnerable save.
• If two neighbouring Force Field Emitters have been destroyed, the force field between the two emitters on either side of the destroyed ones collapses. Units may move across and shoot through this section of the force field as normal.
