Bear in mind that the good schools are usually full, so even if you move into the same street as the school you are unlikely to immediately be given a place. You may well end up with a place on the opposite side of town in a less desirable school until someone leaves.
I would recommend you contact the local authority for advice on available places.
Decent senior schools are considered to be (in no particular order): Denbigh, Shenley Brook End, Hazeley, Oakgrove, Walton Hall and Ousedale. OK but not fantastic ones are St. Pauls (catholic), Stantonbury, Radcliffe and Lord Grey. Generally considered avoid at all cost are MK Academy and Leon, but that's probably snobbery as much as anything.
Niceness of areas tend to follow the school catchments to a certain extent, if your budget is limited try to look for an older area with good school catchments, maybe somewhere like Two Mile Ash, new estates are very expensive (and the houses are tiny). Bletchley is a big area with some nice streets but a lot of it is pretty rough, Newport Pagnell is a lot nicer if you're looking for a proper town rather than an estate.
Oh and MK is pretty multi-cultural, and being mostly new there's a good mix of people rather than enclaves of particular races. In my experience people are pretty tolerant.