What are the longest white slots for? For the new system I plan to get sometime in the future, I have 4 PCI cards I'll need to use but this seems to only have 3... what are the other 2 white slots for?

What MOBO - manufacturer and model! One only knows what sockets you are referring! If it is an old board, then they could be ISA/VESA sockets. If new, I don't know without seeing the board. Usually AGP sockets are tan/light brown and the AGP Pro socket is longer then the standard AGP and there would only be one of those.

sorry... I thought I had attached an image... here it is:

Those are 64-bit PCI slots. Those are going to be the next version of PCI, but I havent seen anything for them in stores yet. If im not mistaken, those can run regular PCI cards, but I dont see how since they are backwards.

Zack is correct, this is a 64bit PCI slot. But becareful, not all are compatible with 32 bit cards. Some manufacturers locked the slot at 66mhz, and is incompatible with a standard 32bit PCI card only running at 33mhz.There are many cards out there, but are limited to 'high end' communication and storage adapters. As an example, the Adaptec 29160 is a 64bit PCI SCSI Host Adapter that will also work in a 32bit slot (it's auto-sensing).These types of motherboards were designed for servers applications.