Took a while, but finally found the help you're after. DL the attached document. Is actually a archived file with a document layer - to extract the drivers (using WinRar), drag-drop file onto WinRar icon/shortcut and extract contents. Either that or open the file in Word and double-click on the rar/zip file image next to the following text on page 2:
Drivers.rar contains FWT Driver files.
If you follow instruction in Doc, you should be right. Apartently there was a delay in getting Vista drivers rolled out for your model, as the chipset designers (Texas Instruments) didn't supply Huawei with Vista drivers for said chipset, which meant they had to build their own... always more time consuming :)