I finally got around to documenting the internal installation of my wake-on-remote module.
http://www.iki.fi/~msmakela/electronics/worc5/#pci
The instructions are for the Hauppauge Nova-T PCI 90002, but I guess that the module could be installed on any PCI card that features a connector for an infrared receiver module. The firmware only works with remote control units that use the Philips RC5 code. Source code is naturally included.
The nice thing in this solution is that there are no added wires outside of the PCI card. The computer will be woken up from the ACPI S5 mode (soft-power-off) by the PCI Power Management Event (PME) signal.
The document also contains instructions for replacing the bundled Hauppauge infrared receiver module with one that works at 3.3 volts. In my case, this about tripled the range of the remote control unit from a few meters to the entire floor.
Marko