1. Disable system restore
  2. Reboot
  3. Run a full system scan
  4. Remove all infected files

If you still have Panda Antivirus installed, you must not remove those files ofcourse :smiley:
Here you can find what is known about Avast detecting infections in Panda files:

http://www.avast.com/eng/support/faq/avast_4_home_profe/virus_detection_and/false_alarm_viruses.html

In general it is not advised to have two different anti virus applications running at the same time.