I took a look inside the case of the FIC Crusader, and the board looks like a fairly standard microATX 1-AGP/3-PCI board. The last PCI slot is taken by a special full-length card that has the PCMCIA slot at its end (at the front bezel), and the header for the firewire, optical and USB ports. The single AGP slot is occupied by a GeForce2 MX.
It should be possible to replace the i845 board with practically any microATX board, with some caveats:
1) The BIOS may not have support for the special PCI card with PCMCIA, firewire, optical and USB (this may only affect boot options, IMHO).
2) There is a ducted fan shroud that envelops the area where the P4 socket (and heatsink) are situated. The replacement board needs to have its socket at the same location, with no components interfering with the shroud. The alternative is to remove the shroud completely.
3) The AGP GeForce2 MX card actually has an S-video connector footprint as well as the footprint for the Philips(?) chip that does the VGA->S-video conversion, but they're not populated, and the end-bracket has no punching for the S-video connector. Too bad that FIC chose to save a few pennies by not providing the S-video capability; however, it should be possible to upgrade the card with one that has the capability, maybe for $100 or so .