A little history on Drunken Merge Parties
This idea was (as I believe) originally developed by a group of ravers in College Station, TX, known as the "Whistle Crew". They coordinated two of these such parties so far (as of January 9, 2001), and both have been considered a jolly good time by all.
What you need
How it works
The final location should be the biggest apartment/house that you can use. If you only have 2 locations, one group goes to the other group's abode. There should be music and drinking games at the final location (DJs and turntables are fun).