My preferred formation and team would be:
4-4-2
Barthez
G Neville O'Shea Ferdinand Silvestre
Beckham Scholes Keane Giggs
Solksjaer RVN
My central defensive pairing is actually Ferdinand-G Neville as I feel Gary is a better centre-half than right-back and a good organizer but since we aren't gonna buy a right-back, this formation will have to do.
I'm not a big advocate of changing formations around to 4-5-1, 4-1-3-2 etc as players will always perform their best if they are playing in their most familiar and comfortable roles.