Take her to the vet to have her checked. False pregnancies do occur, but
real pregnancies should be monitored by the vet in case there are any
problems and to ensure that the queen gets the proper nutrition,
vitamins, minerals, and all that.
The queen should be tested for diseases such as FPV before birthing, as
they can be passed to kittens.

These links might be helpful for you.

http://vetmedicine.about.com/cs/pregcat/
http://www.catclinic.co.uk/health/pregnancy.htm
http://www.sniksnak.com/cathealth/howto15.html
http://www.catsinfo.com/breeding.html

[usenet disclaimer: IANAV. I am not a breeder nor do I advocate breeding
in most contexts. Far too many people irresponsibly breed their cats
already or just neglect to alter them.]