Read thru all of this before trying it. I might have got some steps mixed up when I wrote up these steps since they're partially from memory.
I also have Home Premium Vista on a 64 bit processor. I had a couple of problems along the way, but this is how I got it going, as best as I can remember it.
First I connected the Arduino. I didn't do this next step the first time, but the right thing to do is to tell it not to search for the driver for this device and not ask any more (the third choice on the screen that came up). If you don't do that you'll get bugged everytime the Arduino is connected or the other choice will make you wait until it gets tired of searching Windows Update or you pull the USB cable out of the Arduino. (I might be wrong about the getting bugged every time. because of the second install that I had to go through af the very bottom of this post).
Then as suggested in the previous post I went to control panel -> system -> device manager.
Under "other" there was a device that had a yellow exclamation point by it. Then I get properties for that item by right clicking on it and choosing properties. One of the buttons on the driver dialog that came up was Update Driver.
I don't think I could use the driver that came with the arduino software because they weren't 64 bit. Vista also required that my driver by signed. The most recent version was 2.04.14, but that didn't work because it isn't signed.
The next choice when I looked was below that, 2.04.06. The comment on the FTDI web site says that it is "Microsoft WHQL certified", so I was able to install it successfully.
While updating the drivers, say that you want Windows to look for files on your own computer and browse to the folder that you unzipped 2.04.06. (you go to the folder with the .inf file, not the folder where most of the files are) There were two .INF (install information files) ftdibus and ftdiport. I used ftdiport.
Once I got that done, I had a USB Serial Converter under Universal Serial Bus controls, but it still had an yellow exclamation point warning. Once I rebooted, that error mark went away. My reboot took a long time and I have a fast machine, so be patient on the reboot.
After the reboot I went back to device manager and there was still a yellow exclamation point and I right clicked so that I could go to properties and update the driver. That was real easy because it already knew what folder to find the driver and I just had to tell it to look on my computer instead of search automatically. This one was for the USB Serial port instead of a USB Serial Converter. It didn't ask me to reboot again.
It might be possible to get rid of both device yellow warning messages in one entry to device manager, but that's not what I actually did, so these instructions may not be the most efficient.
Of course, sprinkle the above steps with requests to allow the system to proceed as required.
If I missed any steps, please post a follow-up so that the info gets corrected.
Bill