This could be tricky and it will all depend on when you are planning to move. As you probably know, the system is designed to weed out fraudulent applications, not applications where families have to move for genuine reasons. Provided you qualify for a place within the rules that are specified and you are entirely honest with the Admissions teams (at your own authority and at Bucks CC) at all times you have nothing to fear. The regulations are as follows.
The deadline for providing evidence of your current address is 12th November 2010. That address is the one that is used for allocating a school place. However, please note this point (taken from the current - 2010 - admissions brochure, so subject to change):
If you have been allocated a place at an over subscribed school and move further away before September 2010 the place may be withdrawn. In all cases, you must tell us immediately if you move house after making your application, but before we offer your child a school place. You must also provide evidence of that new address.
That is a slightly confusing statement because it suggests that there are two deadlines - September and March! The School Admissions Code clarifies the position somewhat, as follows (I have edited out points that are not relevant to you):
Withdrawing offers of places
1.50 Once an offer of a school place has been made it is only reasonable for an admission authority to withdraw that offer in very limited circumstances. These may include when a parent has failed to respond to an offer within a reasonable time or the admission authority offered the place on the basis of a fraudulent or intentionally misleading application from a parent (for example, a false claim to residence in a catchment area) which effectively denied a place to another child; or where a place was offered under co-ordination by the local authority, not the admission authority, in error.
1.51 A school must not withdraw a place once a child has started at the school, except where that place was fraudulently obtained. In deciding whether to withdraw the place, the length of time that the child had been at the school must be taken into account, for example, it might be considered appropriate to withdraw the place if the child has been at the school for less than one term.
My advice would be to stay put until September 2011 and to be completely honest at every stage.