A few tests I did...
1) Get from Jeska the latest HUD version (dated May 10th; the older version is from February I think).
2) Attach it.
3) Drop it to the ground.
4) Take it into inventory.
5) Wear it (it should become "Not Available"

.
6) Click on it to make yourself Available.
7) Say "hudreset" (no quotes).

It goes back to Not Available, so turn it available again.
At this step, on the next "greeter panel recycle" (which happens every 1-3 minutes or so), you should be added to the panel. You can at this point upload your image, and if you're at Help Island, you should receive an "ok" in the next "greeter panel recycle" (again, 1-3 minutes).
Sadly, the image won't appear, and there is no way for you to get the notecard working, but at least you will appear on the listing.
To log off properly:
9) Put yourself into "Not Available"
10) Detach
11) Log off from SL.
That way, the panel gets correctly updated.
The next time you log on: repeat steps 1-8.
FAQ:
1) Do I need to go through the whole process every time I wish to be active?
Apparently, yes. The instructions on the HUD say that you need to do a "hudreset" every time you attach it again, for the panel to activate itself with your instructions.
2) Oops. I did something wrong, and I don't show up. How can I fix it?
- Go through steps 1-8, and if it doesn't work, try two or three times. Sooner or later, the panel will pick you up.
- If it refuses to work: drop the HUD attachment on the ground, Edit it, select Tools -> Recompile Scripts in Selection. This is radical stuff, but it should give you a working HUD again.
3) I can't seem to locate Jeska to give me a new HUD, I just have the February version! Will it work?
Probably, yes. Not tested.
4) Oops! I crashed before properly detaching the HUD according to steps 9-11, and nothing works — my name is listed on the panel, but nobody can contact me.
Go through steps 1-8 again. The system knows that you're not really available, so you won't lose any IM requests; it has a timeout feature which works well. As soon as you repeat steps 1-8, the information on the panel should be refreshed correctly.
5) I'm still listed on the panel, I tried to put myself "not available", and/or detached the HUD, but I'm still there! What can I do to remove myself?
There are two possible answers:
- Please be patient! The "Greeter panel recycle time" is usually 1-3 minutes, depending on the lag on HI and the number of Greeters doing the same thing as you. It doesn't happen immediately!
- The panel is now in an "indeterminate" state (see question #4). It lists you but you're not really "there" (ie. people won'pt be able to call you, and your HUD is not really sending any status info to the Greeter panel). To fix it, go through steps 1-8 again.