Thanks. I guess I'm not real clear on when/why to use a web part vs. a control. I dragged/dropped the control in VS2005 and it no longer gives me that error.

So, now I have the Control setup as this:

<cc1:QueryRepeater id="PageImage" runat="server" QueryName="cms.file.selectPageImage" SelectTopN="1" TransformationName="CMS.File.ImageGallery_detail400">
</cc1:QueryRepeater>

With this in the code-behind:
object[,] queryParams = new object[1, 3];
queryParams[0, 1] = "@AliasPath";
queryParams[0, 2] = Functions.GetAliasPath();
this.PageImage.QueryParameters = queryParams;

Now, in my document type query, I have keep getting an error saying the variable @AliasPath needs to be declared:

DECLARE @PathString varchar(200)
DECLARE @ShowDefault char(1)

SET @PathString = @AliasPath
SET @ShowDefault = 'N'

-- This statement loops through the current node's alias path levels until an assigned image is found.
-- If no assigned image is found it defaults to the first image starting with the 'ppl_' prefix.

WHILE(SELECT max(FileID) FROM CONTENT_File WHERE FileDescription like '%' + @PathString + ',%') IS NULL
BEGIN
-- Check if it's the root level. If so, set the flag to display a default image and break
IF(SELECT CHARINDEX('/', REVERSE(@PathString))) = (SELECT(LEN(@PathString)))
BEGIN
SET @ShowDefault = 'Y'
BREAK
END
-- Go back one level in the path and check for an assigned image there
ELSE
BEGIN
SET @PathString = SUBSTRING(@PathString, 1, LEN(@PathString) - CHARINDEX('/', REVERSE(@PathString)))
CONTINUE
END
END

IF @ShowDefault = 'N'
SELECT ##TOPN## * FROM CONTENT_File
WHERE FileDescription like '%' + @PathString + ',%'
ELSE
SELECT ##TOPN## * FROM CONTENT_File
WHERE FileName like 'ppl_%'