yes
Yes.
A "PCI Simple Communications Controller" is usually a PCI modem, but it can be other, sometimes unlikely devices, such as an audio or serial device.
PCI
Typically it is a usb port 2.0.
It means there are two devices trying to use the same IRQ/port number/memory location/whatever (that's what "resource conflict" means). The part about PCI Network Controller means that one of them is, well, the network controller. If you've got a card in a PCI slot, you might try moving it to a different one; also, you might go into the BIOS setup and see if you can change the resource settings there.
Yes, as long as there is an unused PCI slot on the motherboard - usually there are several and often white in color. Also, read the controller's box to ensure your operating system is supported before buying.
NO. If you have a pci-x slot, probably it is a server, and you want to upgrade your graphics card, you can buy a PCI card and plug it into your PCI-X slot. It should work probably.
the slot for the ram
The PCI slot is faster. Offer mayor speed because the PCI use more faster BUSes and new architectures. The PCI EXPRESS is the newest version of the PCI architecture.
PCI, PCI-e, AGP
Host controllers can NOT be downloaded. A host controller for hardware is always going to be a peice of hardware. in your situation, you probably don't have a USB2.0 high speed port. You can always get a USB2.0 PCI adapter.
No. Because the architectures (design) are not equals and the PCI Express have more speed on Its bus.