Seems in the v9.3 OMD you can get a field list of the (I assume) fields involved in the relationship class...
When i try to do it though:
import arcgisscripting
gp = arcgisscripting.create(9.3)
dsc = gp.describe(r"\\snarf\am\div_lm\ds\gis\tools\sde_connections_read\ropa_gis_layer_user.sde\CADASTRE.DOCUMENT_TO_PARCEL") # a relationship class BTW
fieldList = dsc.fields
print fieldList
I just get [] (a blank list!)
Seems like a bug... Maybe it works in v10?