unfortunatly (or fortunatly in alot of cases) linux doesn;t always autodetect things. though it did do that for my sound card. serial ports get set up fine by the kernel and memory does as well. hard drives are added really easily by adding a line to /etc/fstab/ (gives us a ring if you need help with that).
video cards tend to be a bit more of a bugger. you need to have the right package for xfree86 for you card (for example, my ATI Xpert98 needs the xfree86-mach64 package), once you have the right package, you have to reconfigure X (by running XF86Setup or some other config tool).
mother boards should be fine unless its a dodgy type that needs special options in the kernel to work. chips are fine as long as you have the right kerenl for it. so if you have and intel PIII chip and you then stick in a PI (for some bizare reason) you need to have the kernel configured to work optimised for the PI rather than the better types (this setup won;t happen though, just an example. if you got an SPARC chip in their somehow instead then new kernel is in order).
im not sure if the AMD works with the PII optimizations.
Hope that that has answere some of your quezzies