To help you i just looked in "man rpm" and found "--oldpackage" option provides you such functionality. Following sequence works for me

[root@sumit /root]# rpm -q procps
procps-2.0.11-7
[root@sumit /root]# rpm -U procps-2.0.6-5.i386.rpm
warning: procps-2.0.6-5.i386.rpm: V3 DSA signature: NOKEY, key ID db42a60e
package procps-2.0.11-7 (which is newer than procps-2.0.6-5) is already installed
[root@sumit /root]# rpm -U --oldpackage procps-2.0.6-5.i386.rpm
warning: procps-2.0.6-5.i386.rpm: V3 DSA signature: NOKEY, key ID db42a60e
[root@sumit /root]#