Is what free? You forgot to specify.
1 - Is Vista free? No, but it is included with most prebuilt computers.
2 - Is virtualization free? Check out
Virtual Box or
VMware Server.
3 - Is Red Hat Enterprise Linux 4 free? Yes and no. There used to be a pre built instance of RHEL 4 for download from VMware's appliance list, but it seems to be gone. You could download
CentOS 4, which is a RHEL without the Red Hat - it's the same product without costs and with Red Hat's logo's removed, which is per Red Hat's requirement (see, Linux is always free, but Trademarks are different).
Hope that helps.