DATETIME Compare Issue

I am trying to do a select where one set of date/time columns are greater than another. My date is stored in one column while the time is stored in another. Only the date portion of the date column is valid and only the time portion of the time column is valid.
Example my date column value is 8/1/2007 01:01:01 AM and my time column value is 1/1/2007 07:23:49 AM which in my system means the last update time was 8/1/2007 07:23:49 AM.

My select statment looks like this.

SELECT *
FROM CHANGE
WHERE
CONVERT(DATETIME( DATE_LAST_ALTERED, TIME_LAST_ALTERED)) < CONVERT(DATETIME(DATE_APPROVED,TIME_APPROVED))

I get an incorrect syntax near 'DATE_LAST_ALTERED'.

Am I totaly missing the point of DATETIME?

Matt