I was just curious if you could even GET a 0.47uF 500V cap in surface mount, so I did a Digikey search.
The answer is yes, but the only ones I found are ceramic and at $10.45USD each it makes those little transformers start looking pretty cheap.

In through-hole they're available in poly film for about $1 but they ain't particularly small.

I know the answer to Melanies question about 0805 resistor voltage rating. The Vishay parts I use are rated at 150 volts max...

Since you're working on a PIR project, have you seen these?
http://www.zilog.com/docs/devtools/PS0284.pdf
Serial interface to your MCU and can even tell whether something is moving left to right or right to left relative to the sensor. I bought a handful of 'em a couple months ago and am just starting to have fun with them.
I've got parts coming this week to do some serious play with them. Hopefully the UPS man should be bringing me my boards and parts on thursday. Woohoo!


steve