Where I am (Trafford LEA) it works like this:
Each school has a catchment area
The criteria for admissions is set by the school and is usually something like:
1)children in the catchment area with siblings at the school
2)children in the catchment area without siblings
3)children outside the catchment area with siblings
4)children outside the catchment.
Where they reach the point of not enough places, this is how the allocate and say they got to step 2) and didn't have enough places for all those kids, they'd do it by distance from the front door of the school to the front door of the child's house drawing a straight line on an OS map (you can see I've done my research )
In terms of applications:
To apply to a school for which you are in the catchment area - you apply directly to the school by the start of the Easter holidays before your child would start in Sept.
To apply for a school for which you are not in the catchment area - you apply to the LEA by January of the year your child starts school.
When you put their name down is irrelevant - admissions work on the criteria above and not on a 'first come first served' basis.
DS1 starts our local school in Sept 2005 and I've not put his application in yet as we aren't moving into our new house till January so will wait till then.
BUT, I think you need to ring your own LEA to find out as it looks like it's slightly different in different LEAs. It is certainly different in this LEA among the schools as the catholic primaries have slightly different admissions criteria to the normal state schools.