Are you creating a custom form? If so, you can easily output the field
value without using a form field.

If not, there are some creative solutions out there:
http://www.google.com/search?q=sharepoint+default+form+read+only+field

Just to view the ID field on any view can be done as follwos:

Go to List settings and click on any view (say "All items") for editing. On the
edit view page
check the box for ID and it will display ID on that particular view.

Also: If you do need to grab the ID and assign it to another custom field for
display, you can do so by creating a simple SP Designer workflow.

You are trying to make the ID field show up on the EditForm.aspx or the
DispForm.aspx? Obviously you can't make the ID show on the NewForm.aspx
because it hasn't been assigned yet.

If you want to do this on DispForm.aspx, for example, go to SPD2007 and
open the DispForm.aspx in Split mode. In the Design view right-click the
default web part and choose Web Part Properties. In the Layout section
select the checkbox to hide the web part. In the Code view put your
cursor immediately after </WebPart></WebPartPages:ListFormWebPart>. In
the menu select Insert-->SharePoint Controls-->Custom List Form...

Select your list, make sure you are using the correct Content Type for
your form (Item is default on Custom Lists) and select the "Display item
form" radio button. Select OK. That inserts a DataFormWebPart.

Go down to the <tr> where you want to insert the ID row and use this
code:
<tr>
<td width="190px" valign="top" class="ms-formlabel">
<H3 class="ms-standardheader">
<nobr>ID</nobr>
</H3>
</td>
<td width="400px" valign="top" class="ms-formbody">
<xsl:value-of select="@ID"/>
</td>
</tr>

Save and go. I hope this was what you were looking for...

This is exactly what I was looking for. I am trying to modify the
DisForm.aspx.