The .ics form of the BCG calendar is in an industry-standard calendar format (“ICAL”) readable by nearly any modern calendaring application. Here are instructions on what do with your downloaded file for some popular applications.
Google calendar: On your calendar page, in the lefthand sidebar, click the arrow to the right of “Other calendars”, and select “Import calendar”. Choose the location where you saved the .ics download, choose the calendar you want to import it into, and click Import.
Yahoo! calendar: If you are logged into the same Yahoo account as you use for GuildGuild, you don't have to do anything! This calendar has already been imported into the GuildGuild calendar, so just check the box next to it in the “Yahoo Groups” section of your calendar list to overlay it on your calendar. (Otherwise, for any other Yahoo account, choose “Import” from the drop-down menu next to the calendar you want to import into and proceed as above.)
Outlook 2010: If you have let Outlook be the default calendar manager, so that it handles .ics files directly, just open (double-click) the .ics file. Outlook will open the file and add it as a separate calendar. You can keep it as a separate calendar, or you can “overlay” it on your regular calendar by clicking the subtle arrow at the top of the calendar. Alternatively, you can import the .ics events directly into your regular Outlook calendar (regardless of whether it’s the default calendar manager), by using Outlook’s Import wizard (File | Open | Import).
It should be something like that for other calendaring systems, too.
If you’re unsure about how it’s going to come out, simply create a new calendar, import into that one, and see how you like it. If it’s good, then throw away that calendar and import it to the calendar you really want it in.
And since .ics is a plain-text format, you can also edit it before importing it to do a global find & replace if you’d like the events to be named differently.