Newbie question about SNMP

Hi everyone

Can anyone help me to solve this problem?
Im using a script to show a table with interface information in Cisco
Routers equipments.

When I use the command below
snmpwalk -c <community> <host> interfaces.ifTable.ifEntry.ifDescr.5

I receive the message:
no MIB objects contained under subtree

but if I type this:
snmpwalk -c <community> <host> interfaces.ifTable.ifEntry.ifDescr
the ouput is similar to this:
interfaces.ifTable.ifEntry.ifDescr.1 : DISPLAY STRING- (ascii):
Ethernet0/0
interfaces.ifTable.ifEntry.ifDescr.2 : DISPLAY STRING- (ascii): Null0
interfaces.ifTable.ifEntry.ifDescr.3 : DISPLAY STRING- (ascii): E1
0/0
interfaces.ifTable.ifEntry.ifDescr.4 : DISPLAY STRING- (ascii):
Serial0/0:0
interfaces.ifTable.ifEntry.ifDescr.5 : DISPLAY STRING- (ascii):
Loopback12

The first command only works if i use it as root, but for security
questions i must use it with another ordinary user
In the same way I need to be a root to execute the command like this
snmpwalk -c <community> <host> ifDescr.1

Can anyone tell me why is that so?

Thanks in advance
Luis