1. A feature dataset is also a workspace, so set your feature dataset as the environment workspace.
2. Iterate through each feature class in the workspace and delete it.
I don't have ArcGIS 10.0 but in 9.3 it looks like this:
Try this in 10:
gp = arcgisscripting.create(9.3)
gp.workspace = r"C:\workspace\fileGeodatabase.gdb\featureDataset"
for objFeatureClass in gp.listfeatureclasses():
arcpy.env.workspace = r"C:\Temp\fileGeodatabase.gdb\featureDataset"
for objFeatureClass in arcpy.ListFeatureClasses():