Safely use old windows XP machine in business network

It is not that uncommon to have these out-of-support and vulnerable machines in an organisation. It's important to perform a risk assessment to determine the impact of any vulnerabilities.

High-Level Risk Assessment

Threats:

• Internet connections mean that remote threats are a problem
• Local network connections mean that threats within the network (or remote threats that have gained access to the network) are a problem
• Local physical access to the machine means that anyone who can interact with the machine can be a problem

Impact:

• Network connections mean that the machine can be used to attack the rest of the network.
• Any access means that any sensitive data on the machine is at risk (if there is sensitive data on it, like manufacturing designs)
• Any access means that configurations or machine settings can be maliciously (and dangerously) changed

Mitigations:

• reduce or eliminate network connections
• reduce or eliminate physical access to the machines by unauthorised people

Your Specific Case

Without knowing more specific requirements for the machine in your company:

If you need Internet access (and it truly cannot be replaced by some other measure) then you need to cut it off from the rest of your network as much as possible and only allow it to receive connections only from the manufacturer and blocked from making connections out. Your perimeter and internal firewalls come into play here to design a new network. You also want to be able to monitor and recover from any anomalies that occur on the machine.

What I have done in similar situations is to turn the machine into a Virtual Machine (VM), and use VM tools to snapshot, revert, etc. and use the hypervisor to control access, networking, and monitoring. Virtualising the machine is not always possible, however.