Is there any way to tell if a motherboard can use one of these cards to flash a 360?

I was just wondering because my PC has an onboard SATA but it won't detect my drive so I am going to get a PCI card and install it on my older computer from like 2000/2001 and I was just wondering if there was any chance it would not be able to be used with that PC?

No, but incompatibility is very rare, sometimes you may need to move the card to a different PCI slot (Due to IRQ sharing or something like that), but other than that it should work just fine.

Last incompatibility issues I've seen were about AGP graphics cards (was about AGP 4x / 8x and 1.8V / 3.3V AGP slots or so) and a Asus P5A (Ancient) on which you shouldn't use TNT based graphics cards (or so).

afaik all sata chipsets can be used to flash drives as long as you remove the drivers and install portio. the vcc trick will not work on f.i. a sis900 chipset, but it can be used to flash 360 drives. in your case you might have some driver issues, just remove them. off course this is not an option IF you need these drivers to boot windows..... (i don't need them, since i boot windows of an ide controller). but the same for the pci addon card, don't install the supplied via drivers. only install portio driver, then let the flashing begin.