Unable to establish Secure Network Connection with HP DV9500

I have an HP DV9500 that has sat idle for some time. When I first bought it back in August of 2007 I networked it with my Dell XPS 410 using my Linksys WRT 350N Gigabit modem's wireless settings, and was able to establish a secure connection. However, there was a strange glitch that every time I had the laptop turned off, the printer wouldn't work (it was like the printer thought the laptop was in charge of the network). Eventually, as I wasn't using the laptop much (mainly bought it for an extended vacation we took in September and October of 2007), I took it off the network and just turned it off and let it sit here for a year or so, as I seldom need a laptop, and it's just me and my elderly mom and I was never able to get her interested...

Anyway, she finally found a long lost friend several states away who is online, so now she's interested in it. Since then, Vista has gone through SP1, so I needed to get the laptop all updated, and since I was having a difficult time getting it hooked into the network, I mainlined it into the cable modem at first, to get everything updated (took FOREVER to get my network working again!). At any rate, while I can now get it to do an UNSECURED network with no problem, as soon as I try to turn on any type of network security, the network connection disables. I've tried doing it from the Desktop side, both wirelessly, AND by using a USB flash drive and transferring the settings that way -- at least a dozen times -- to no avail... I've tried EVERYTHING I CAN THINK OF on the laptop -- every single setting I can find on there... every single network and internet setting I can find on the desktop and/or for the router, as well, including resetting the router -- No Dice.

I don't know if SP1 changed something, or what. I'm certainly not going to give this laptop to a novice user with an unsecured wireless connection. I wouldn't use it that way, much less have a novice use it that way. I had it turned off again for several weeks trying to think through this. Just turned it on again earlier tonight and let the UNSECURED connection last long enough for Norton and Windows Update to finish, then tried applying WPA2-Personal security, and as soon as I clicked "OK" my connection died... Since then I've tried the other "flavors" of security, but none of them works, either.

There's a message in the "Connect to a Network" box that says, "The settings saved on this computer for the network do not match the requirements of the network." Of course clicking "Diagnose" is a complete waste of time. The ONLY thing that works is turning off all security, and then the network connection will work again. My network is still secure between my modem and the internet, because I have security set up there, as well, but with Wireless N, that signal's strong enough that anyone within close proximity could be picking it up, monitoring, whatever.

Does anyone have any thoughts? This system is under extended warranty, but I can't find anything wrong with the computer. When I run a check of compatible modems, the modem I'm using isn't on the list, but I just find it hard to believe the modem is the problem -- especially when it DID work with this modem 1.5 years ago.

Any suggestions will be greatly appreciated!
Jeff