As far as I know it started when Zandig got himself and Wifebeater for some tryouts with BJW and it kind of started into an "invasion" angle.
Though, sadly, CZW wasn't as good as it was today as it's wrestlers and the company itself hadn't evolved to what it was in it's peak of 2002 thus a majority of the matches weren't all that good.
The relationship ended offically after the BJW Ante Up PPV when Zandig won the BJW Deathmatch Heavyweight Title from Matsunaga in an Exploding Glass Ultraviolent Deathmatch before saying that CZW put BJW on the map (which obviously is total crap as BJW has been around for four more years than CZW) and leaving with the belt.
Though in some positive aspects they managed to try out some of the more unique stipulations that were on the minds of CZW's and BJW's creative team.
Tarantula Deathmatch (which was good for the freak value)
200 Light Tubes Deathmatch
Barbwire Canvas Deathmatch
The first ever Fans Bring The Weapons Deathmatch in Japan
Fire Deathmatch w/ the wooden boards exposed
Salt, Mustard & Lemons Deathmatch