hi,
i got a rescue cat which turned up at my work (a kennels) one day and didnt leave, fink sum1 abused her and dumped her at gates coz she was in bad way. we all named her 'spit' for the obvious reasons and cudnt get near to her. every spare min i got id go and sit near her with my hand out, talking gently but not making eye contact (threatening for cats) and eventually, she came to me for the odd stroke. in the end, i ended up taking her home as she got cat flu and needed round the clock care.
keep the new cat in one room which is quiet and not too big. i did this, and it allowed her to get used to the new enviironment, and i gradually increased the area she was allowed into. a year on, shes great with me, but still extremly nervous of my dad and not so much my mam and isnt at all bothered by the dog!!
time and patience is the key, and soon enough theyll come around. am now building her an enclosed are ain the garden to get her used to noises outside before letting her out on her own.
hope some of this helps. oh, and try pilchards in tomato sauce to get cats to eat, they love it!!