Gene,
Good points. I just think that while upgrading to a Gb can't hurt, I am not sure it will solve your problem. A new switch (managed if possible) can be helpful. One weak link can cause issues. For instance, a NIC that is not set to autonegotiate can be a problem. Nice thing about a managed switch is that you can look and make sure everything is at 1,000.
Wireless is fine. I just know it is always slower so I brought that up and you had mentioned it in your previous post.
This could be a simple issue or it may be many things. I would try that change on your main computer to background services. That was recommended by a very high up and knowledgeable IT network person.
I still think that the most bang for your buck would be hiring a network IT (preferably a Microsoft MVP) to spend a day (probably at $75 per hour) and watch what is going on at certain times of the day. What appears to be a Gb setup may be only 10 if you aren't set up correctly. Rob, my IT friend, said he went into a large telephone company and found tons of issues that were slowing it down.
When it does start to slow down see how much RAM SQL is using. Look at the error and log files (I can't think of the right word) on the main computer.
Good luck. Troubleshoot one thing at a time. Think about this. You started with issues around a year ago. All this time you were frustrated when a super sharp IT person may have fixed things right up.
I can't say a server would make a huge difference. And, it is expensive. But, a domain is a hell of a lot more fun than a P2P, trust me.
Oh yeah, my post count has little to do with my computer knowledge, although I do have a little. I admire that you are working through this as much as you can on your own.
