Intruder Alert?

This by itself simply suggests a network misconfiguration somewhere, but I'm not enough of an expert on this topic to help you find it.

Regarding the shady tech guy - why did you have to ask him to leave? If he was simply an incompetent, he could have messed up your network settings, causing this problem. However, if you believe he may have had malicious intentions, you may want to consider running [MacScan|http://macscan.securemac.com>. Ordinarily, I consider that software to be serious overkill, due to the inclusion in their malware definitions of many legit tools that merely have potential to be misused. However, in your situation, that could very well be the case.

What kind of router do you have? Do you know the username/password to log into it? It sounds like there's a DHCP issue, either something's up with your router that's handing out addresses, or you have a computer on the network set to use a static IP and the router isn't aware of this, so it also tries to give out that address thinking it's available. If you've changed the SSID/password for wi-fi, then I wouldn't worry about someone trying to hack in, DHCP is not usually what people go after anyway.

I'd check your computer and your husbands, in network preferences make sure they're both set to use DHCP and are not set to manual IP addresses.

Well if you've verified that all of your devices are set to DHCP (not manual or DHCP with manual address) for all interfaces they may be using, then it kind of sounds like your router has a flaky software issue with DHCP.

Certainly, if your wi-fi is not password protected, there's always the possibility that someone may be trying to use it and could throw a wrench in the system, but let's be honest, most people have no idea how to launch a DHCP starvation attack, and would have no reason to do so to a home user.

I might log in to the router and poke around to see if there are any static mappings or DHCP configurations in place other than the default, make sure your router isn't using an address in the DHCP pool, etc. (most routers are smart enough to know not to try and give out their own address but you never know). If your router config is pretty simple you can always do a factory reset according to the manufacturer's instructions and reconfigure it (last resort). Otherwise, the next time the message pops up, let us know the exact wording, that might help a bit.

k.panic, is there any way that you could login to our router and poke around?

That is not possible unless you have enabled remote administration, but even then, what you're asking is the height of foolishness! You don't know anything about k.panic, or anyone else here, but you're trusting him enough to give him access to your home network? That's very, very bad. (No offense to k.panic, who I doubt would actually hack your router.)

We also want to hire someone to tell me how to setup a static network behind my router so our Apple devices and printer work without massaging every time we want to use one.

You need to hire someone local, affiliated with a reputable company, not an unknown from an internet forum.

No, I'm sorry, that's not something I can do. :-\

uPnP is Universal Plug 'n Play, that's fine if it's on. HNAP is a Cisco remote management protocol, I've never used it, if it were my router I usually would turn stuff like that off if I know I'm not using it.

Honestly you shouldn't need to set up static mappings unless you have specific devices that you know would work better with one, like a printer that each user gets to by way of IP address; such a device would need to have an address that never changes, but for most things like a computer accessed via Bonjour, you'd never need to know what the IP address is because Bonjour takes care of advertising your computer on the network for you.

So what do you think could be causing the "in use by another device" errors?

I would guess the static IPs assigned to the iPads and iPod Touches is causing it. I've got three iPod Touches on my home network, with dynamic IPs, and all works fine.

What gave you the idea that I have static IPs assigned?

Because you said:

I was told our Ipads and iPod Touches, with also intermittent connection problems, would work better with static IPs.

Ghjeesh!

Not sure what that's about...

PamsPlace, I had the very same problem and, having consulted on these forums, decided that the most likely explanation was a fault with the router. I checked and found that the router Firmware was way out of date.
Upgrading to the latest Firmware Version appears to have solved the problem but as the fault was intermittent I will need to monitor it for a little while to be absolutely certain.