i have installed a virtual rhel 6 on a host rhel 6 system...(i am preparing for the rhce exam) but i am not able to ping them with each other.

please help

You asked for immediate help, that might not be possible here. Google is best for immediate help.

which virtualizing software are you using?

If you are on Virtualbox, you might have to add the guests to a local ethernet lan in the network settings.
I have been using Virtualbox in preparing for my rhcsa/rhce exam. And all I had to do was to add them in to the local lan, it's nice to have one bridged guest with on for internet access in case you need to update some software. And for the proxy part of the book.

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You're using RHEL6...call them, they're there for "immediate help", since you're paying for RHEL, right? Otherwise, GardarS advice is probably right on the money, but you don't say WHAT virtual machine you're using.

When studying for the Red Hat exams, I recommend that you use KVM. It's the --only-- virtual machine (VM) solution supported by Red Hat for RHEL 6.

When you study KVM, you'll learn about commands like virt-install for setting up installations, as well as virsh for managing configured VMs. With the possible exception of Xen, you won't learn how to use these commands with any other VM solution. (Although Xen is supported in earlier versions of RHEL 5, current exams are based on RHEL 6.)

If you're having these network problems with KVM, one approach is to make sure that networking is properly configured in the Virtual Machine Manager. The default network is configured on 192.168.122.0/24. Unless you've changed the default and/or have set up a second network, you'll need to make sure that all KVM systems are configured on 192.168.122.0/24. Otherwise, you won't be able to ping between two VMs on that network.