Thank you both for the warm welcome!

I've been lurking around for a while now. Sounds creepy when you say it that way...Regardless, I'm just starting my MAME project, and it's going to be a while before it's done. Progress is slow because the wife has stipulations about selling this before I can buy that etc. HA!
Anyways, I'm slowly putting my plan together, getting all the emulators working, and acquiring some parts. It's going to be a 4 player upright cabinet. One of my prime motivations for this project was to have a working 2 player light gun cabinet. I wanted it to have real arcade guns. I happened to see the HAPP 45 caliber guns and see that they were discontinuing the "deep purple" model. So, before I knew if I could actually use them with MAME, I bought the guns.
I've since scoured every thread on every message board I could find to try to see if there's a system of any kind that will allow me to use my guns with MAME. I read a lot about the Opti-Gun adapter, and saw all the negative comments (that were mostly speculation), but I did find one thread that had an interesting post. It seems as if the folks at Nanotech who made the opti-gun adapter sold it to Global VR who renamed it the usb2gun. A forum member here called dmarcum99 claimed that he has the board and that it works great with his setup. See this thread
http://forum.arcadecontrols.com/index.php/topic,82460.msg1209063.html#msg1209063 He didn't have much more to say on the subject, but I would like to ask him a couple of specific questions. Since then another member (lodoss118) had bought the board, but could not get it to work right. I suspect though, that that might be because he was trying to use a Namco gun. If you look at the original opti-gun specs, it says that it works with HAPP and Betson/Imperial guns. Furthermore, if you can dig up and OLD thread where Mr. David Foley from nanotech was talking about the product pre-release, he mentioned that some guns were not compatible. Hence my desire to ask dmarcum99 a couple things about his setup!
I know a lot of people seem to be recommending the Aim-Trak system from Ultimarc, but that doesn't seem like a route I want to go if I can possibly find another way. I've carefully watched every video I can find, read everything I can find, and come to the following conclusion:
1. It seems that this system is not actually accurate to where you're aiming, but is only accurate to the extent that you can move a cursor around. I want to aim with gun sights, not with a cursor. I have a Wii, and that's not the experience I'm looking for. It's 2 different ways of playing a game. I was a 3DO Mad Dog McCree maniac. I want real arcade light guns!!!
2. I'd rather not hack up the insides of my (now discontinued) purple HAPP guns if there's any chance that a real light gun solution will be available in the future.
I have seen a recent thread about integrating a camera instead of the LED sensor bar to make the aim-trak more accurate and better functioning. I might be able to convince myself to go that route if it was the ONLY way, but I want to exhaust all other possibilities first. I also don't want to screw up my bezel with a sensor or camera.
It's funny. All of the amazing creative solutions that people have come up with, but this one seems to just be the one nobody can figure out. I understand that many people have LCD screens now, but the games that I want to play were originally designed for a crt screen with light guns, and that's how I want to play them again! You'd think if the ACT Labs guns could function even halfway decent, that someone could come up with an interface board that would actually work. Some of the people on this forum seem to be able to solder up their own personal nuclear reactor out of some bits of wire and a couple resistors, but yet here I am holding two HAPP guns with nothing to shoot them at...