I have the same problem and it is so annoying, I have tow ways to solve it (restart and the other one), but maybe we all are in diferents scenarios. In my case started to happen since I have my computer with IIS7 serving a aspnet web page and almost all the time and when it happen to me I am developing something with VS2005, I notice if you start the "ASP .Net Development server", 100% of the times all the browsers start to work again, yes I know is weird, all the times I had this problem it worked for me.
But I am sure the VS2005 is not the problem, cuz I've working with it several years and never happened, and now it happen even if I am not using it. So right now I am looking for the solution on internet, but if I cant find it I will have to investigate for the services and applications that this server reset or start, cuz I know that could help to fix this problem.
If someone already have the fix for this please let me know, I am tired of this Issue and I cant find the problem, If someone have somthing in commun with me, let me know (IIS7 working and VS2005, same Win Vista as you mentioned).
If I cant find something, I will try to find for my self and share with you all ;) ... I hope there is another one and I didnt notice, cuz I dont want to complicate my self. :p
So, if works and is easy to you, Run the "ASP .Net Development server", when you have this problem
In my case I run this command:
start /B %WINDIR%\Microsoft.NET\Framework\v2.0.50727\webdev.webserver.exe /path:"D:\MyFolder" /vpath:/HelloWorldWebSite
You have to create a shity website to use this thing, but when you have the problems every day a lot of times and you cant reinstall windows, you consider to do this stupid fix.
but it is soooooo annoying do this only for this thing, but I prefer this and no reboot my machine... gosh!! I am tired and I have to SOLVE this in a decent way. No this, but by now is the only one I have.
If someone find something let me know, I will do the same :)
Rolo, from CR