Hi,
 
Somebody please tell me, does 8800 GTX supports any motherboard with a PCI Express slot? or are there any other conditions?

The 8800GTX will not fit in any PCI-e slot actually.  It will only fit in PCI-e X16 or PCI-e X16 2.0.
 
But it will fit in any motherboard with the available slot.

Thanks.

Make sure you have a good PSU.

Thats right, good PSU and good case. If the case is short, then that' s really a big problem for you.