I'm using Quark 4.1. Make sure in your colour palettes, the colour you selected is spot colour, not CMYK or any non-spot process plan.
then when outputting, setup up (in print dialog) the 'document' tab to separations on, and then in 'output' tab, 'plates', setup 'process and spot'- you'll see the spot colour you specified in the dialog. Then print out the postscript, distill it and when you view it in reader etc., you'll see the plate for spot if you use the process viewer....
regards
vinland