And the interfaces would be...?
Voodoo or not, a code is no good without the code book.
Always look for the following:
Case:            ATX or Micro-ATX or E-ATX
Motherboard:  ATX or Micro-ATX or E-ATX
Micro-ATX works in 
Most ATX cases.  ATX will 
not work in a Micro-ATX case.  E-ATX I don't know anything about.
Motherboard 
Socket: AM2 or AM2+ or AM2/AM2+ or AM3 or AM2/AM2+/AM3 or LGA 775
CPU 
Socket:            AM2 or AM2+ or AM2/AM2+ or AM3 or AM2/AM2+/AM3 or LGA 775
AM2 works in AM2+.  AM3 works in 
most AM2+ boards.  LGA 775 Will 
Not Work in any AM# Slot, as AM# is AMD and LGA is Intel.
Motherboard 
PCI:  PCI or PCI-E x1 or PCI-E x16 or PCI-E x16 2.0
Video card 
PCI:    PCI or PCI-E x1 or PCI-E x16 or PCI-E x16 2.0
Must match, although I know of no PCI-E x1 Cards.  
This go in order of least performance to highest.  The only "must match" exception is PCI-E x16 and PCI-E x16 2.0, they are compatible with each other, 
but a PCI-E x16 2.0 in a PCI-E x16 will not work as well.
Those are the most important to match up, and easiest to mix up.
With Power Supplies make sure you see:500Watt (or greater) with: 20+4 Pin/24Pin  -  6 Pin and 6+2 Pin  -  4/8 Pin  -  and a good brand name such as PC Power and Cooling, OCZ or SeaSonic.
Then you get in to things that are less serious if mixed up:
Hard Drive: IDE or SATA (motherboards support both)
DVD:         IDE or SATA (Same)