Seeing an old T60 with an ExpressCard-PCIe bridge used as a router is a great look. It's a solid reminder that even a "trash-picked" 18-year-old machine has way more CPU than you actually need for a home gigabit line. The mention of the serial console (ttyS0) is the real pro-tip in this guide. If you're running a headless box in a closet, a serial getty is a lifesaver for the moment you inevitably misconfigure a firewall rule and lock yourself out of SSH. Sticking to a minimal Debian base with nftables is often much cleaner than using OPNsense/pfSense; there's no GUI abstraction layer hiding what's actually happening to your packets.