You have couple of options.
I think the simplest is if you use Django 1.2, then you have to create custom form for your admin and use 'widgets' option:
ProjectForm(forms.ModelForm)
    class Meta:
        model = Project
        widgets = { 
           'field_1' : forms.Textarea(attrs={'class':'ckeditor'}),
           'field_2' : forms.Textarea(attrs={'class':'ckeditor'}),
            ...
        }
If you use older version of Django you can still use custom form, just override the field, in which you want ckEditor, in the form:
ProjectForm(forms.ModelForm)
    class Meta:
        model = Project
    field_1 = forms.SomeField(label=u'my label', widget=forms.Textarea(attrs={'class':'ckeditor'}))
Alternative:
ProjectForm(forms.ModelForm)
    class Meta:
        model = Project
    def __init__(self, *args, **kwargs):
        super(ProjectForm, self).__init__(*args, **kwargs)
        self.fields['field_1'].widget = forms.Textarea(attrs={'class':'ckeditor'})
Finally for all three options, you set your ProjectAdmin to use ProjectForm:
class ProjectAdmin(admin.ModelAdmin)
    form = ProjectForm