Sorry you have hd such a hassle - we have a wireless as well and have a couple neighbours who have very lax security and I made it a point to let them know (fotunately, they are also friends and were thankfuk for the advice - one did not even have a password!!!).
You've already rec'd some good advice so I will just add mine anbd you can opt
what to choose to do: (and I would also ask for help from Linksys -they do have good tech support and also talk to your isp);
1. Turn off SSID Broadcast. As someone already suggested tjo using other language, most of the factory or company defaults are alrready knoqwn and crackers ore phishers can get them if they do not. (ie the bad guys). Leaving SSID on is like leaving your garage door open with all your valuable in it, cars, snow blower, etc, etc.... and use a really difficult password, nothing simple!!! DSomething that takes time to crack! And I am assuming you have encrypted WEP.
2. Implement MAC security but you have done thatr, right?
3. There are some technqiues we do just to keep the would be intruders confused (and we live near so many universities that I woud not at all surprised there are many would be "attackers" on our wireless's doorstep so to speak. (Tho students are hardly the ones one needs to worry about, it is the crooks that are the problem. These include mocing around the router - so it is not always in the same place.
4. Don't restrict the 192.168.1.x as a Class C subnet for IP nos. You could split up the local network into network segments using subnet classes tho some say this can be accesses by ppl who are determined to get in as well, sigh.
Not sure of this will help but there is an article here:
Finally, what does your ISP say about this? Do you check each night so that you know who has accessed your computer and then go after them or at least give their IP numbers to someone. I had someone with some page I just accessed with Internet Explorer and its isecurity allowed this program -and every program, file that is on a site ends up on your hard drive and some of them are malware and can take over your computer,. This one did that in spite of all my precautions. I figured out his IP number and went after him - virtually,, not personally, lol (he was a "businessman" - using the term loosely - in Montreal - wioth contracts to create ads for some pretty credible compaies like Sears so I wrote to them and others and to him. (I was more than a Reverse DNS lookup to say the leasyt but I think it is always good to know who is accessing your computer, whether you have wireless or not).
I would gather all that material - with the relevant programs and go to the police with them. It is still break and enter, however you cut it even tho new law is being made even as I type.
Finally, by far - given how fast the crooks catch up - the best protection now is WPA2 encryption so check to see if your router and all of your wireless computers and devices support it.
You can always turn it back on them - if they access your wireless, you ha ve access to their passwords and so forth!! Go after them, again not by yourself but with legal help.
I hope this helps - it is all so basic I know, I wish I could give you more but there is more info out there that can hekp. Talk to the ppl at Linksys and other security companies.