Cant setup an Alfa external usb adapter with Vista

I have a Dell Inspiron 1720 running Vista with service pack2.  I use the computer to connect to a wifi system on a mobile home site in France where the signal is weak.  I have bought an Alfa AWUS036H USB adapter since this is highly recommended to improve reception in difficult areas.  It is also possible to connect an external antenna which I cant do with the inbuilt Intel adapter card. I have tried a number of different ways of installing the adapter and its associated utility and whilst it appears in 'Device Manager' and says its working and that I have the most up to date driver it will not connect to my home router.  I have disabled the built in Intel adapter but still it wont connect.  I suspect there is a conflict somewhere but I do not have the expertise to know how to establish that. I know the Alfa USB adapter works because I have successfully installed it on my Dell Mini 10 running XP so maybe it is Vista which is causing the problem.  I have tried the Alfa website but it does not offer much help. Has anyone experienced any thing like this?  I would greatly appreciate some help. David

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