Nothing complex about it.
When you click the link it sends you a vcs file.
That file contains a calendar event for outlook.
As windows has everything integrated into one big "thing" your browser immediately opens the file with outlook. When outlook reads the file, it adds the event to your calender.
this is one of the events from the site you mentioned:
BEGIN:VCALENDAR
PRODID:-//Microsoft Corporation//Outlook 9.0 MIMEDIR//EN
VERSION:1.0
BEGIN:VEVENT
DTSTART:20010116T220000Z
DTEND:20010117T120000Z
LOCATION;ENCODING=QUOTED-PRINTABLE:See Details
UID:040000008200E00074C5B7101A82E00800000000A0A9911F2807C0010000000000000000100
00000B262E2001973D411BA130050046C6256
DESCRIPTION;ENCODING=QUOTED-PRINTABLE:The Gigabit Ethernet - Speaker from Yipes Glen Waring (Director of Sales).=0D=0APlease join our discussion: The Original Ethernet, Public Ethernet Network, Typical Carrier Infrastructure and Limitations,and Future Gigabit Ethernet Networks.=0D=0A=0D=0A6 PM Reception, complimentary hot and cold appetizers.=0D=0A=0D=0ALocation: Ft. Lauderdale Marriott North (Take I-95 to Cypress Creek Rd, go north on 6650 N. Andrews Avenue - the Marriott will be on your right) (954) 493-5307.=0D=0A=0D=0AMembers are $15 ($10 with RSVP 48 hours before event)/Non-members $20 ($15 with RSVP 48 hours before event).=0D=0A Please RSVP
SUMMARY;ENCODING=QUOTED-PRINTABLE:South Florida Telecom Forum
PRIORITY:3
END:VEVENT
END:VCALENDAR
