searching multiple types of data properly

[la...@gmail.com]

hello,
 I'm storing book information in my lucene index. i want the user to be able 
to search the book's title, isbn, and author all in one query without him 
having to specify which of the 3 types of information he is searching. i 
further want the user to be able to mix the information in the search so 
that if he wants, he can put parts of the title and author's name in his 
search. For this reason, i didn't split the book information into separate 
fields and kept it all in one field because if i were to use a multiple 
field query, the scoring will not be accurate. however, since i'm adding all 
this extra information into one big field, if somebody types "Da Vinci" and 
if i have 2 rows with the following information: "111111111 Da Vinci Code 
Dan Brown" (for "Da Vinci Code" by "Dan Brown") and "2222222222 Da Vinci 
Mike R Jones" (for "Da Vinci" by "Mike R Jones"), then they will return the 
same score because they are equal in length. This is not the behavior i'm 
looking for because if somebody typed in the exact title of the book, then 
it should mean more than typing in only part of the title. 
 what is the best way to go about this? 
 thank you 
greg