Chad,
If you run the caps in series, the capacitance will be cut in half. However, you *must* use a resistive voltage divider to assure that the caps each see exactly half the voltage. Place something like a 100k resistor (the value isn't critical) in parallel with each capacitor. A 1/2W will be sufficient.
The reason is that the voltage will divide across the caps in proportion to their actual capacitance. Given that electrolytics are notorious for being +-20% on their capacitance value, the results will be unpredictable, and could easily exceed the voltage rating for one of the caps. The resistors will force the voltage to divide evenly.
Tube folks do this all the time. In the first leg of the Pi filter in my amps, I've got a couple of 350V caps in series (with resistors, of course) in order to create an effective 700V cap bank for a 575V rail. I could have used two 300V caps, but 350V parts came my way cheaply, and I couldn't say no.
Grey
[Edited by GRollins on 09-26-2001 at 08:38 PM]