Detailed long events in iCal

Lets say there's a 4-day conference, all day event, i add it to my iCal calendar. Is there any way to add additonal subevents to this event, like certain keynotes? Of course i can add them as new events but then i have no way to differentiate them from other events happening at the same time that have nothing to do with the conference.

Is there a way to do this in iCal? How about Entourage?

 

No, I'm not talking about WWDC, I actually need it for some LAN parties and music festivals. Creating a new calendar isn't a good solution for two reasons:

1. It would mess with my semantics, currently different calendars represent different categories of events (band, university, work, private, ...), adding a calendar for ONE event would break this system.

2. I can't afford to add so many calendars - if there is just one such event every month, I'll end up with 20 after a year (already got 8 calendars), which is totally incomprehensible (too many colours ).