They did however remove the original, DreamWeaver post - lucky for me someone remembered & posted about it.
To add insult, the problem was caused by registry keys under ie's User Agent key, had to be put back for ie7 to work properly after install, & was reported with DreamWeaver CS4 Beta, yet Adobe neither fixed it or included it in the list of known problems. CS4 installation problems are common enough that Adobe has set aside a section of their site just for that, & their forum search, where I eventually found an answer, is ridiculous - filtering doesn't work correctly, so I had to wade thru pages of post headings, reading anything that sounded promising before I found the cure. the DVD for CS4 doesn't even include a PDF manual, & there's no book included. Some things it seems you can only do in P/Shop - it can really help with DVD menus in some authoring programs, in fact DVDA makes it harder on you if you don't use it.