No, you must accept the fact that the sudoku is solved even you can't see the numbers. The really important question here is make a creating routine which cheks the rules for sudoku and doesn't finish until it gets a solved sudoku. As I said, in the ps2 this could take up to three minutes (because of the ps2 limitations) but the fact is that placing numbers randomly, you'll finally get a solved sudoku.. dosn't matter how many time takes to do it.
Once you have created the sudoku and stored in a matrix, you can show the numbers you want, just as if you were doing the sudoku in a paper with a pencil, you can draw numbers and erase and try all you want but the solved sudoku is stored and that doesn't change.
In my code I did it this way: (I'm gonna explain you cos' the code is buggie with the emu but gonna try post soon)
1) Create a solved sudoku... SOLVED! or anyway it wont never be created.
2) Hide all the numbers. (Hide for the player but still there stored!)
3) Decide how many clue numbers to show acording the difficult of
the game.
Those numbers are choosen random and doesn't matter how
many of them you show or where are placed because the showed
numbers dosn't change the fact that we have stored a solved
sudoku.
The only thing that changes by showing less clue numbers
is that the player may have not enough clues to be sure 100%
if a number is in the right place and would need to try different
posibilities until get enough info to decide, but remember!! The
player my not be sure of a number, but of course THE PROGRAM IS
because solved sudoke is stored.
Think that even if you show a EMPTY BOARD the sudoku could be
solved anyway... cos it is actually SOLVED BUT YOU CAN'T SEE IT
Hope you understand and start tryin'. I'm gonna share the sudoku creator as soon as posible to show hot it works and it is
100% ERROR FREE. The really important question of the sudoku creator is this: BE SURE THAT ALL THE SUDOKU RULES ARE CHEKED AND PASSED anytime you place a random number, so the creator will
be "trying" to create sudokus until it finally gets a solved sudoku, and think that the random numbers the creator is trying to place are just temporary numbers and are permanently cheked and deleted until all the number passed the rules, then the sudoku is created, the numbers became FIXED AND STORED.... and you... can do what you want... showing some of those number or no one at all.
The player can also place numbers in the board... but in a different matrix for not to lose the data of the solved sudoku... mess around, place numbers, delete... the player can do anything.
Although not able to see... THE SOLVED SUDOKU IS OUT THERE...

See you! If your really interested in sudoku creator keep an eye around and i'll post something soon.