There's a site - the 'good schools guide'. You have to pay a small amount but not much (couple of pounds a month I believe). It has info about schools and catchment areas and all that kind of thing.
There are also some sites which give you info about the area you're thinking of living - up my street - is one and there was a police one that went live about a year ago but I can't remember what it is called - gave info on recent crimes and that kind of thing. A bit freaky for some by all accounts, but interesting

Grammar schools are alright (I went to one), but not great if your kids aren't particularly academic - they're very university geared (or at least mine was when I was there and I imagine it still is). Don't rule out the local secondary school if it's got a decent ofsted report. Grammar schools usually have an entrance test (even if your children are too old for the 11+ exam) - you can check out 11+ questions online - I did that a while back and was surprised at how hard some of them were..........I must have been smarter back when I was 10

Most schools have websites now - you can find more info about applying from there and sites like the good schools guide. I'll be joining that site myself in the next 6 months or so.
Also rightmove dot co dot uk is useful for checking out house prices and also which schools are in which area - then you can narrow it down using ofsted and the other site I mentioned.