Easiest way for the PHP challenged among us might be to use the Mail Merge feature of MS Word. Create a template in Word with this format that reads the different fields from the Excel file.
<GroundOverlay>
<name>XXXIMAGE NAMEXXXX</name>
<visibility>0</visibility>
<Icon>
<href>XXXXFILE LOCATION OR URLXXXX</href>
</Icon>
<LatLonBox>
<north>XXXNORTHXXX</north>
<south>XXXSOUTHXXX</south>
<east>XXXEASTXXX</east>
<west>XXXWESTXXX</west>
</LatLonBox>
</GroundOverlay>
Then just export it as a plain text file.
One thing to also consider is whether you want an index of the maps to show up in Google Earth. Take a look at the KMZ file that I made attached to this topic for some options on how to do an index.
http://bbs.keyhole.com/ubb/showflat.php?...&PHPSESSID=The folder caled "Historic Topos - 15" has one type of index system and the folders with "NEW" at the end use a different index system. They both have advantages and disadvantages, but I prefer the one that uses placemarks instead of polygons.
Also, remember that the size of your source images are important. If they are bigger than 2,000 x 2,000 they won't work very will in GE.
Matt