out of memory error when running DB maintenance

I have a DB taking up 220gb of a 300gb drive so I purged some old data
from it. When I try to vaccum/analyze using pgAdmin III I keep getting
an out of memory error. I am running Windows Vista 64 bit with 8gb of
RAM and I have change the postgresql.conf file variables to the following:

#custom_variable_classes = '' # list of custom variable class names
shared_buffers = 1024MB
effective_cache_size = 2048MB
work_mem = 64MB
maintenance_work_mem = 1024MB
commit_delay = 10000
checkpoint_segments = 128
checkpoint_completion_target = 0.9
wal_buffers = 2MB

Any ideas on how I can avoid running out of memory and run a successful
vacuum/analyze?

Thanks,
Ben