A collaring ceremony can be anything from just the two of you in a private room to a full blown wedding style ceremony. There are no hard and fast rules for collaring. They can be as fanciful as you wish them to be online or they can be deadly serious. Within real life, collaring also vary greatly but the most common generalized ceremony is outlined below. It also seems to be the most common that I have seen online. It is modeled after some d/s groups' real life ceremonies.  

The participants are the dominant who is going to collar, the submissive who is to be collared, a master of ceremonies, and the presenter of the collar. Extras can include a sort of best man or maid of honor for each side of the couple.  
  

     Normally what happens is the dominant stands beside the master of ceremonies and the submissive kneels  before the dominant.  

     The master of ceremonies then gives a small address to the guests, usually about the special nature of a D/s relationship, the strength of the bond and the meaning of a collar.  

     The master of ceremonies then asks the dominant a few questions, usually along the lines of ensuring the dominant is aware of and agreeing to their responsibilities as a dominant.  

     The master of ceremonies then asks a few questions of the submissive usually including a statement of free will, and to ensure the submissive is aware of what they are getting in to.  

     The master of ceremonies then takes the collar from whoever is holding it, and presents it to the guests so they may see it, then hands it to the dominant.  

     The dominant then shows the collar to the submissive, describing it and speaking a few words of what the collar means to them asking the submissive if he/she accepts the responsibility of the collar.  

     the submissive now has an opportunity to speak, usually a few words of their devotion commitment and love  (get that a lot on IRC) their understanding of the responsibility the collar entails, and their willingness to meet those responsibilities to the best of their abilities  

     the dominant then places the collar about the submissive's neck..  

     the submissive changes nick to reflect the collar..usually a capital letter or two enclosed in brackets at the end of their nick..jane{D}  

     the ceremony can then be ended with a symbolic gesture of completion..a kiss, or the attaching of a leash to  the collar.. 

For such a formal ceremony, it is a good idea to plan it in advance. And for the master of ceremonies to make their speech into popups or macros. It is also a good idea to have a run through a couple times before the actual ceremony takes place. It is also helpful if all the participants in the ceremony use the same server at the time of the actual ceremony, this helps cut down on possible lags and splits.