Thans for that advice, d, but I decided to try that link I found on the Mediatek Website first.
And it's worked! I am typing from the PC as we speak having installed the file.
This thread has now popped up as a Google Search Result for 'TP-Link T2U Vista' for for anybody clicking into this thread welcome and this is what you have to do...
1) Go to
http://alumni.mediatek.com/en/downloads1/downloads/usb/ which is the link for the driver - it asks you for a name and email address but any text in and email address format will do
2) Download the file which comes up as IS_Setup_ICS_011916_1.5.39.173.exe
3) Run the file - you have a choice of just installing the driver or the config program as well (I just selected the Driver)
4) Once run you can plug in the TP-Link adapter and Vista recognises and installs it.
Just run a Speed Test on thinkbroadband.com and got 50.8Mbps (matching my supposed broadband capability).
Thanks for reading...