20+ years of AIDS and no vaccine, why?

It's been over twenty years since Robert Gallo's announcement that he'd discovered the probable cause of AIDS. In the U.S., we've spent over 100 billion dollars researching HIV. Worldwide, there are over 100,000 researchers poking and prodding this retrovirus. Margaret Heckler announced in 1984 that a vaccine would be available within two years (1986). So many researchers, so much time, so much money...it's 2005, where's that vaccine?
There are two important points to consider with HIV and vaccines. First, how do vaccines work? To most laypeople, a vaccine must seem like an almost magical fluid that gets injected into a person and voila, they're cured. Vaccines don't cure anybody of anything, not directly anyway. Unlike drugs, which are designed to disrupt, interrupt, alter or terminate certain cellular functions, vaccines essentially help the body help itself. A weakend, or altered form of the virus we're trying to combat is injected into the body. The immune system recognizes this presence as an invader and sets about creating antibodies against it. So far, so good.
The second point to consider is how we go about diagnosing HIV infection. Everybody knows that we use an antibody test to determine HIV positivity. So...we assume somebody's HIV-infected because their blood reacts to an antibody test, which obviously means they're naturally producing antibodies to HIV. Back to the vaccine! So how would a vaccine-induced antibody response differ from one induced by HIV itself? How would a weakened/altered form of HIV entice the immune system into creating better antibodies to HIV than the ones it produces against the real thing? Anybody notice a problem here?
Pretend for a moment that a vaccine against HIV has been made. You get injected with it, and soon your body starts producing antibodies to HIV. Ok, no problem. At some point in the future, you come into contact with HIV. Your immune system notices this invader, and with it's previously-acquired HIV antibodies, sets about to eradicate it from your body. How is this different from people today who are HIV positive (by the finding of HIV antibodies) whose immune systems are doing just what they're supposed to be doing...producing antibodies against HIV? It seems quite paradoxical that an immune system can be vigorously producing antibodies against a pathogen and still be viewed as fatally crippled. Immune systems produce antibodies, that's what they do. If an immune system was overwhelmed or devastated by a pathogen, a good clue would be that it wasn't able to produce antibodies.
So, somebody please tell me how a vaccine against HIV can be created. If our bodies and immune systems are already doing what a vaccine would help do, what's the missing part of the equation?