Problem verifying BIOS signature

I am having problem verifying BIOS signature.
I get this warning:
gpg: WARNING: This key is not certified with a trusted signature!

I think problem lies somewhere with this line:
Command> sign
gpg: no default secret key: secret key not available

What am I supposed to do to get rid of that warning?
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Here is exactly what I did:

# gpg --import linux-security-publickey.txt

gpg: directory `/root/.gnupg' created
gpg: new configuration file `/root/.gnupg/gpg.conf' created
gpg: WARNING: options in `/root/.gnupg/gpg.conf' are not yet active during this run
gpg: keyring `/root/.gnupg/secring.gpg' created
gpg: keyring `/root/.gnupg/pubring.gpg' created
gpg: /root/.gnupg/trustdb.gpg: trustdb created
gpg: key 23B66A9D: public key "Dell, Inc. (Product Group) " imported
gpg: Total number processed: 1
gpg:               imported: 1



# gpg --edit-key 23B66A9D

gpg (GnuPG) 1.4.5; Copyright (C) 2006 Free Software Foundation, Inc.
This program comes with ABSOLUTELY NO WARRANTY.
This is free software, and you are welcome to redistribute it
under certain conditions. See the file COPYING for details.


pub  1024D/23B66A9D  created: 2001-04-16  expires: never       usage: SC 
                     trust: unknown       validity: unknown
sub  1024g/10C11901  created: 2001-04-16  expires: never       usage: E  
[ unknown] (1). Dell, Inc. (Product Group)

Command> fpr
pub   1024D/23B66A9D 2001-04-16 Dell, Inc. (Product Group)
 Primary key fingerprint: 4172 E2CE 955A 1776 A5E6  1BB7 CA77 951D 23B6 6A9D

Command> sign
gpg: no default secret key: secret key not available

Command> quit


# gpg --verify PE2950_BIOS_LX_2.6.1.BIN.sign PE2950_BIOS_LX_2.6.1.BIN

gpg: Signature made Thu 18 Jun 2009 04:39:07 PM CDT using DSA key ID 23B66A9D
gpg: Good signature from "Dell, Inc. (Product Group) "
gpg: WARNING: This key is not certified with a trusted signature!
gpg:          There is no indication that the signature belongs to the owner.
Primary key fingerprint: 4172 E2CE 955A 1776 A5E6  1BB7 CA77 951D 23B6 6A9D