Adobe uses the adobe download manager to install and update its software. It hasn't worked on the last two XP machines I have. It tries to update or download, produces a meaningless error message (server is unavailable, the file has moved etc) and tries again. Eventually I kill it.
I used to be able to get the full installs when updates were needed and by pass this dysfunctional software, but that's no longer possible.
Ok, I think to myself, I'll just download a new version of Adobe Download Manager. Except, you can't.
Adobe has created a loop. A broken install of ADM means you can't update or replace ADM. Despite Adobe's claims that I can remove it, I can't do that. (I suspect our corporate distribution of Adobe Acrobat Pro broke it on both machines.)
Acrobat is a strategic product for Adobe. . If they can't get the updater right they can't get anything right. Adobe is not doing well.
 I removed Adobe Reader from my Mac for other reasons -- it was annoying and badly behaved. ADM on the Mac did work, though it had oddities too I believe. Adobe has never been able to figure our permissions on OS X, which does not bode well for Vista.
9/25/08: The solution in a later post might be worth applying in this setting. I haven't missed Adobe Reader/Mac since I removed it, so I can't test. Adobe's OS X software is pretty much an insult.