The CCK parameter let you insert one of your CCK field in full. This parameter, cckteaser, let you insert the teaser of your CCK field.
This feature uses the teaser flag of the CCK module in order to insert the teaser data. This means only the field_<name> fields make the distinction between cck=... and cckteaser=..., the other fields simply ignores the difference.
For more information on the CCK field names that are supported, check the Insert Node Parameter: cck (6-1.2) page.
IMPORTANT NOTE
Note that the parameter value ends with a semi-colon! Do not include quotes unless you want to see them in the output. Yes. This means the text cannot include a semi-colon as is. Since CCK field names should not include semi-colon, you should have no problem.
This option requires the CCK module to be installed. When it is used without the CCK module installed, the Insert Node module output an inline error letting you know that you need to install and enable the CCK module.