Well, you could do something like this:
Say your radio buttons were like
<input type=radio name=catagory value=A> Catagory A <br>
<input type=radio name=catagory value=B> Catagory B <br>
<input type=radio name=catagory value=C> Catagory C <br>
Then, you would have your other search fields. Then you could have a PHP script like so:
dbconnect(); //You should make some kind of function for connecting to the database, and then use the correct one
if ($catagory == A) {
//Search the table for catagory A
}
elseif ($catagory == B) {
//Search the table for catagory B
}
else {
//This means the catagory is C, so seach the table for catagory C
}
Hope this helps!