I have a related (not duplicate) post on the sharepoint group, but I
think the solution to my problem lies somewhere with XSL.
Unfortunately, I only know XSL from reading SharePoint views - which is
to say that I'm not too familiar with it.

Related SharePoint Post:
http://groups-beta.google.com/group/microsoft.public.sharepoint.windowsservices/browse_thread/thread/1af90c78bb4ede62/e4655adb54b93376

What I think I need to do is to modify the XSL of the data view so that
the filter parameters - currently set to filter off of URL parameters -
are omitted if the URL parameters are not present.

Example:

I go to http://mysite/List/all.aspx?ID=123 should filter the list to
show only records relating to item #123.
If '?ID=123' is not present, I want to show everything - which is the
default behavior of the view.

In the data view, I have the following code which I belive is
responsible for filtering the list.

** How (XSL syntax) can I conditionally apply the filters? **

<dsp:Where xmlns:dsp="http://schemas.microsoft.com/sharepoint/dsp">
<dsp:And>
<dsp:Eq>
<dsp:FieldRef Name="Graphic_x0020_Type"/>
<dsp:Value Type="x:string">Awards Detail</dsp:Value>
</dsp:Eq>
<dsp:Or Group="true">
<dsp:Or>
<dsp:Eq>
<dsp:FieldRef
Name="Related_x0020_Project_x0020__x0028_1_x0029_"/>
<dsp:Value
Type="x:string"><udc:ClientParameterValue
xmlns:udc="http://schemas.microsoft.com/data/udc"
Name="filterParam"/></dsp:Value>
</dsp:Eq>
<dsp:Eq>
<dsp:FieldRef
Name="Related_x0020_Project_x0020__x0028_2_x0029_"/>
<dsp:Value
Type="x:string"><udc:ClientParameterValue
xmlns:udc="http://schemas.microsoft.com/data/udc"
Name="filterParam"/></dsp:Value>
</dsp:Eq>
</dsp:Or>
<dsp:Eq>
<dsp:FieldRef
Name="Related_x0020_Project_x0020__x0028_3_x0029_"/>
<dsp:Value Type="x:string"><udc:ClientParameterValue
xmlns:udc="http://schemas.microsoft.com/data/udc"
Name="filterParam"/></dsp:Value>
</dsp:Eq>
        </dsp:Or>
    </dsp:And>
</dsp:Where>