I eventually solved the problem, with help from HRT's Kevin Halverson. It was worth the effort. The microStreamer sounds better than my PC's sound card.
When I plugged in the microStreamer's USB cable, Vista attempted to load a driver for it. It failed to find a driver on my computer; it tried to find a driver at "Windows Update" and failed again. I tried this 4 or 5 times and it kept failing.
I found an email address for support at HRT's website; Kevin answered my email within 5 hours, even though it was a weekend. He said that every installation of Vista supports the USB Audio Class 1.0 standard, straight out of the box. He recommended that I get out my official install discs. My copy of Vista is legal, but I bought it with a name brand PC, so I have RE-install discs. I plugged in the microStreamer again, and when Vista failed again, it prompted me to insert a disc, so I tried the Vista RE-install disc. It failed. I repeated all this again, and pointed it at the PC manufacturer's disc of drivers. It failed again.
I did some research which revealed that Windows Vista Home Basic stores drivers in this folder:
Further research said that Vista's support for the USB Audio Class 1.0 standard is provided by a physical file called Usbaudio.sys. Since my folder was lacking that file, I eventually found and downloaded it from www.sysfiles-download.com to my Downloads folder.
I was not able to copy/paste the file into the correct FileRepository folder.
I told Windows to Search for new hardware. It eventually said it could not find a driver and gave me the option of Browsing. I Browsed to the Downloads folder, but the wizard quickly reported that it could not find a useful driver for the device in that folder.
Before giving up for the night, I unplugged the provided USB cable and plugged it back in. Inexplicably, Vista understood the microStreamer immediately.
I am enjoying the HRT microStreamer. Thanks, Kevin!
Columbus, Ohio, USA