Webform rules: compare a form field to a user field
I guess that you can enable Rules Forms support Submodule of Rules. This submodule shows the correct name of your form (above each respective form) to be used with Rules.

Also, see this answer, is related with Rules Forms support submodule and other steps to make a comparision form fields with rules, I think that could be useful.

Update: This is the address to download the module Rules Forms support for Drupal 7 http://drupal.org/project/rules_forms

this is an screen shot in Drupal 7 about when is enabled rules for a specific webform: