so what does this mean now for 2010 mac pro owners?? Does this mean certain software won't be able to run on these new mac pros. They talked about drivers, drivers for what exactly, but I don't really think I understand all of this.
Perhiperals like Firewire, USB, PCI-e devices sometimes comes with pieces of software that "drive" the communication between the Mac and the add-on device. For example printers have drivers.
Some drivers are written by Apple. Typically those are generic. The more non generic funcitionality your add-on device has the more likely it needs a special driver. Another set of drivers are collected by Apple and distributed with system updates. Apple just ships, not writes them.
Likewise some things make low level kernel modifications ( e.g., Cicso VPN tweaks how packets get routed onto network ). So some cases not necessarily a physical device.
The crux of the matter drivers generally have to tightly integrate with the OS kernel. So if make major change to kernel ( go from 32 to 64 bits ) you have to change the drivers.
What will happen with 64 bit kernel is that potentially printer, PCI-e , etc. will stop working because that company hasn't released updated 64 bit versions of their drivers. That's not really a big issue at this point. With the Snow Leopard release most manufacturers got on board with 64 kernels for their then current offerings.
The big problem tends to be someone who is pushing old legacy cards/printers/etc. that aren't supported anymore. The 64-bit kernel will likely send them over the edge into not working mode. They'll need to replace or just simply boot 32-bit all the time.
Folks would bought highly specialized, low volume equipment are usually more freaked out about this. If you attach relatively modern and mainstream stuff to your Mac you probably have no issues with either kernel version.
The vast majority of Applications just "talk" to the OS. The don't require kernel modifications. The 32-bit kernel can run the more common 64-bit apps (all other macs ship exactly in that mode) and the 64-bit kernel can run 32 and 64 bit apps transparently. So no big impact at the app level. As long as they don't dip into the kernels internals the mode of the kernel shouldn't really matter.