77,

You're right. The ABS & O2 sensors are in no way inter-related and should not be coming on at the same time. Focus on the O2 sensor situation first since the ABS lite being on will not effect braking performance (some members (me included) prefer it with ABS disabled).

It sounds to me like you may have a grounding issue within your guage cluster. Your ABS light has probably been triggered for a long time but hasn't been coming on due to a bad ground. When the CEL comes on, it provides the path to ground for the ABS lite to actually illuminate. That's just one possibility in a long list of gremlins that may be causing your issue.