Ok, my cat is 1 and she just gave birth to her second litter last week and she is doing fine and so are all 4 kittens. You will notice as you say her nipples getting larger, her tummy will get bigger and because cats only carry for 9 weeks it all happens pretty quick! If she laying sleping you may see the kittens moving around and kicking inside her, you can usually see this from around 6 weeks. Also she will be looking for a place to "nest" so if you dont want her having them on your bed or in the airing cupboard then maybe place a few boxes around with some newspaper and an old towel in and hopefully she'll get the hint to have them in there (mine did) - thanks god! Lol!
One other thing i will say is when she goes into labour be with her and for every kitten make sure there is an afterbirth (its like a sack of red blood cells) and the cat will eat it and detatch the kitten from it!
I think i touched Summer's first litter too soon and she lost the scent off them but she did abandon them and they did die (but it was my fault for touching them, not the cat), im not saying that this is going to happen, im just saying dont touch them for at least a week because you never know and keep them on the blanket or towel that she gives birth on - they need the smell as they are born blind and dont open their eyes until 7-10 days.
Hope this is all helpful and i didnt ramble too much there is some really good sites on the net - just google "pregnant cat" that should help!
Anything else i'll try and answer for you
Sarah