My apologies.

The approach is different for version 5.x.

You will need to edit the following file:

\CMSModules\MessageBoards\Controls\Messages\MessageEdit.ascx.cs

To remove the fields, you need to hide each field and label, disable the required field validation, remove the error message for the field, and not add the field to a validation group.

For example, to remove the name field, do the following:

1. Within the SetupControls method, add the following lines:

lblUserName.Visible = false;
txtUserName.Visible = false;
rfvUserName.Enabled = false;

2. Comment out these lines:
rfvUserName.ErrorMessage = ResHelper.GetString("board.messageedit.rfvusername");
...
txtUserName.ValidationGroup = valGroup;
rfvUserName.ValidationGroup = valGroup;

The name field should no longer be required.