A plain text based database The list of the files on my hard disks has grown up to a million, the more or less, of records, each consisting of a eigth or ten fields, es.
support id - file size -  full path name - md5 hash - sha256 hash

All is stored in plain text files realized with the DOS's DIR command.

I must restructure the archive (suppressing unwanted redundance, organizing backup procedures ...), therefore I need a (free for personal use) database system, running under Windows Xp, able to perform simple queries on  the file resulting from the unification of aforementioned lists (or import it) and exporting the result as plain text or XML.
In the past, I have unsuccessfully tried Microsoft Access. 

I have no need to share or publish the dataset, because it is for my personal use only.

Please, can you suggest any suitable software ?

Thanks in advances !!
I'm no huge fan of Microsoft Access, but I'd be curious to know why you were unsuccessful at it.  It should easily be able to hold that information and is probably easier to learn than other RDBMS systems.
Having said that, I think either MySql or Sql Server Express would work great.  You would use a text import process (Sql Server has a wizard that makes it easy), bring all the data into one table and then dedup and organize anyway you see fit.  

1 million rows with 10 columns wont be a very large table, my guess is it will be somewhere near 500Mb.