You are mixing ColdFusion variables (which cfif requires) and SQL column names. Think of it this way, all CF tags and function execute before the SQL query is sent to the SQL server. You're mixing this and trying to run the CF statement on the SQL server and thus the failure.
You need something like this:
<cfquery name="GetPastEvents" datasource="DSN">
SELECT *
FROM SITE:Calendar
WHERE DatePart('yyyy', [StartDate]) = <cfqueryparam value="#Dateformat(Today, 'yyyy')#" cfsqltype="CF_SQL_DATE" />
and (
(enddate is not null and EndDate < <cfqueryparam value="#Today#" cfsqltype="CF_SQL_DATE" />)
or (enddate is null and StartDate < <cfqueryparam value="#Today#" cfsqltype="CF_SQL_DATE" />)
)
and Archive = <cfqueryparam value="0" cfsqltype="CF_SQL_INTEGER" />
ORDER BY StartDate ASC, StartTime ASC
</cfquery>
Also, I think your cfif logic was backwards. Instead of NEQ I think you meant EQ because having an EndDate EQ '' and then comparing EndDate to Today (else clause) doesn't make sense.
