I dug through my files and found this site:
http://www.dr-addie.com/WhatIsFIP.htm#Wet%20or%20effusive%20FIP
It gives loads of information on both the wet form and the dry form of FIP. I'm awfully sorry to hear that you and your kitten are dealing with this. I have no personal experience with this disease, so unfortunately I cannot offer anything more than the advice to Google it to learn as much about it as you can, and my concern and sympathy that you are having to experience this.
Ghilly
http://www.animalhealthchannel.com/fip/index.shtml
The above link is a very very inclusive description of F.I.P. Saying kitty is a "poor doer" is probably the vet's way of saying your cat is in a fairly symptomatic state. The link (I think) has a support site connected to it. If not, let me know, I'll see if I can hunt it up.
Sorry to hear about your ill kitty...I wish you both luck.