assuming that after downloading the driver and you double click it with your mouse and it fails on installation. I would perhaps suggest the following.
At work we recieved a vista machine and wished to install an epson stylus photo 2100, which whilst there was vista drivers available for it off the epson site, they would fail to install, sighting that it needed some particular epson file that the Vista version of the driver appeared to not have.
I solved the issue by doing the following.
I downloaded a previous OS system driver other than the Vista version which was WHQL certified and installed that first. e.g. NT, 2000 certified. Once that installed I then attempted to install the vista version of said driver, which proceeded to install and the stylus 2100 worked fine.
If appears to be taking a long time to install the vista driver, give it time, the epson vista drivers do appear to take a while to fully install.