Mail Merge Dropping Leading Zeroes

Using Excel 2007 and Word 2007, I created a mail list in Excel formatting the
5-digit zipcodes as ZIPCODES and the 9-digit zipcodes as ZIPCODE+4. When I
previewed and printed the merged data, I saw the zipcodes with a leading zero
had the zero truncated (ie 02035 printed as 2035) and the 9-digit zipcode
printed as a 0. I temporarily resolved the problem by changing all 0-prefixed
zipcodes with '0 to make it a text field. I defined the 9-digit field as TEXT
also. Anyone else encounter this problem? Any suggestions how I can fix this?
Thanks in advance for any advice given..
--
Bob B
.