A blue bulb won't give you the most light though. It may look brighter, but going through the filter to make it blue will cut down on the amount of light that actually makes it out of the bulb.
The HID headlamp assemblies from a newer Seville will fit, but they are veery expensive, because they include the bulb and ballast assembly. If your really looking for HID's, I would suggest a good aftermarket company. They are easy to install, and are very reliable, in most cases more reliable than OEM equipment. That what I did on my 1998 STS. Also, if you do go for HID's, they are different temperature ratings, depending on how much light you want, and what kind of color. The coolest bulbs (i.e. 4-5000 degrees kelvin) will produce the most actual light output, and will be very white. The higher you go in temperature (i.e.7-8000 degrees kelvin) the bulbs will produce a blue light, with a little less intensity than the cooler bulbs. At the end of the scale (i.e. 12-14000 degrees kelvin) the bulbs are now producing purlpe light, and have much less intensity than their cooler counterparts.