One idea you can do is use some virtualization software (VirtualBox is free, but I pay the C-notes for VMWare Workstation because it has a lot more features, and is the de facto standard), and put your older applications in a virtual machine.
The advantage of doing this is that when you upgrade hardware, you just copy the VM's files from the old box to the new box... the older application and its environment never has to be modified, and is secure from hack attempts because the VM software can be configured to "hide" the VM from the outside world using NAT (network address translation.) Another advantage is that one can use snapshots and back those up.
A small business I help out has a very creaky old version of some specialty software which will not run on anything newer than XP. Since the software never touches the Web, and only accesses a shared directory, it sits in a virtual machine configured with no network adapters, and has been moved from physical machine to machine for a number of years now. So far, so good. Periodic scans of the VM's virtual drive files have shown it to be clean of any nasties.
