This and many more tips are available in the FAQ noted below.

For an example you could use:

|;
if (($per_admin) or (!$in{'modify'})) {
print qq|
<TR><TD><$font>Field 3</font></TD><TD><INPUT TYPE="TEXT" NAME="Field3" SIZE="10" VALUE="$rec{'Field3'}" MAXLENGTH="10"></TD></TR> |;
}

for each field that you only want admin to be able to modify.

Unoffical DBMan FAQ

http://creativecomputingweb.com/dbman/index.shtml/