The No 1 seeded teams from each of the six nations - England, Ireland, Italy, France, Scotland (Edinburgh Gunners) and Wales (Cardiff Blues) - will be drawn in separate Pools.
Five of the Pools will have no more than one team from the same country. One of the Pools will have two French teams as France have earned an additional seventh place by virtue of being the most successful nation out of England, Italy and France in the 2005 / 2006 tournament.
The date, venue and additional details of the draw will be announced shortly
Two more clubs - Benetton Treviso and Rugby Calvisano - have booked their Heineken Cup 2006 / 2007 places by qualifying for the Super 10 final to be played at Stadio Brianteo, Monza, on Saturday, 27 May.
And Newport Gwent Dragons, highest non-qualifying team from the Celtic nations, will play Overmach Parma, the best of the losing Italian semi-finalists, at Rodney Parade, Newport, on Friday, 2 June for the 24th and final position.
The match will kick-off at 7.45 pm and will be televised live by Sky Sports and S4C.
The second Scottish place is still up for grabs between Border Reivers (currently ninth in the Celtic League) and 10th placed Glasgow Warriors while in France the seventh place will be filled by either Castres Olympique (currently seventh in the Top 14) and ASM Clermont Auvergne, who are in eighth spot.
Border Reivers are home to the Dragons and Glasgow travel to Connacht on Friday night in the Celtic League while Castres travel to Pau and ASM Clermont go to Bayonne in the final round of the Top 14 on Saturday afternoon.
The 21 qualifiers so far (by country in alphabetical order) are:
ENGLAND (six of six): Gloucester Rugby, Leicester Tigers, London Irish, London Wasps, Northampton Saints, Sale Sharks.
IRELAND (three of three): Leinster, Munster, Ulster.
ITALY: (two of two): Benetton Treviso, Rugby Calvisano.
FRANCE (six of seven): Agen, Biarritz Olympique, Bourgoin, Perpignan, Stade Francais Paris, Toulouse.
SCOTLAND (one of two): Edinburgh Gunners.
WALES (three of three): Cardiff Blues, Llanelli Scarlets, Ospreys.