Help Required To Find Out When A Cluster Has Failed Over.

I am writing a little systems monitoring application to send SMS
messages to my mobile phone. For example when disk space reaches a
certain maount my program will raise an alert that fires a VB app,
that sends a SMS message directly to my mobile.
We operate an active/active cluster (SQL7 NT4) and I want to be informed
when one of the clusters fails over.
I have managed to find out when the clusters are 'off-line' by reading
the 'PersistentState' variable from the registry as follows:

DECLARE @LIVE_REPonV1 varchar(8000)
EXEC master..xp_regread
@rootkey='HKEY_LOCAL_MACHINE',
@key='ClusterGroupsd42a2a2d-f6a5-11d4-a584-00508bdfa98a',
@value_name='PersistentState',
@value= @LIVE_REPonV1 OUTPUT
SELECT convert(varbinary,@LIVE_REPonV1)

this has a value of 0x01000000 for on-line and 0x00000000 for
off-line.

However, after scanning the registry I cannot find a registry variable
that resembles a 'failed-over' status.
Any help would be most appreciated.