I am stumped. I tested ODS HTML with the minimal style in both 8.2 and 9.1.3 and I -do- get gridlines when I open the HTML file with Excel 2002. I do NOT have Excel 2000 to test with.
This seems like a problem that can be best solved by Tech Support. The only other thing I might suggest is to issue this statement:
ods path sashelp.tmplmst(read);
before your ODS HTML step and see if somehow a changed version of styles.minimal has gotten into your ODS PATH.
Other than that, you can find out how to contact Tech Support at the following link:
http://support.sas.com/techsup/contact/index.html
cynthia