1. Many machines can run vista. You may not be able to run it with all of the eye candy turned on, but you will be able to run it with any up to date machine.
2. You would be surprised what you can run Photoshop with. It's just a matter of how quickly you want to complete tasks. Tablets are trivial where resources are concerned, as the most common ones(Wacom Graphire or Intuos models) are USB. If you're seeing a slowdown from a USB input device, you've got other problems. The only exception would be something like a Cintiq, but I highly doubt that's what you're talking about. If it is, you need to rethink that area a little bit.
3. Personally, I like nVIDIA stuff. However, the performance crown shifts back and forth between ATI and nVIDIA.
4. You do not have a Creative Analogy 4. You have a Creative Audigy 4. Given your games selection, it's way overkill for anything you're going to be playing.
5. From what I've seen in passing, any major name brand adapter will be compatible with Vista.
Please realize that you are running a less than optimal configuration by using a user's PC to share a connection, as opposed to a wireless/wired combo router. That's what routers are for: dedicated connection sharing.
6. Don't buy things based on their connections on the front panel. If it's such a killer issue for you, a USB hub is cheaper and easier to position where you can reach it(and a one time setup when you first assemble the machine anyway). If you're just talking about one flash drive, you might as well use a simple USB extension cable.