How to update all the values in a Dictionary<string, bool>

I am using c# vs2005 compact framework.

I need to update all the values in the dictionary to false.

foreach (string key in parameterDictionary.Keys.ToList())
  parameterDictionary[key] = false;

".ToList() is not available" in compactframework. How can i loop and update.

Can any one suggest the way to update all the values in a dictionary.