I have a content type which has a large number of fields, for example:
By default, when a user adds a new node, these fields will appear one under the other. I want to change the layout, and place the "last name" field to the right of "first name."
Can you tell how I can implement this? Is there a module I can use?
Here is a great tutorial on how to theme a node edit/add form in Drupal 6: Theme a CCK input form for CCK2 & CCK3
You can use Panels Module for this. Using Panel you can entirely modify the way a node should look like when viewed or edited.
For that:
There are multiple layout options for your fields.
You have view modes for selecting which fields are shown in which mode.
You can use CSS overrides in your theme to float right or left the fields.
Design Suite is specifically created to arrange fields within the content area of a page, like, into columns, or rows.
Yes, Panels is overkill for such a small task, but it gives you a very rich environment with a future. Panelizer is the easiest panels way to duplicate the Design Suite functionality of arranging fields in columns
You can use Display suite to arrange the layout of your fields in a predefined or custom layout. The effect will be similar to the panels above.
However, for this particular use case, you don't really want to use layout regions, but you want to merge these fields inline.
This can be done with custom formatters or with display suite custom fields. The basic idea is that you have one "field" on display level, that displays the values from both fields from the database level.
I will not elaborate much further, because there is already an excellent answer over here: https://drupal.stackexchange.com/a/41167/2974
