The progression of the head-to-head suggests that Berdych should win this match by a "6-3 6-3"-like scoreline.
Sweden Clay F Nadal 2-6 6-2 6-4
2005 ATP Masters Series Cincinnati
Ohio, USA Hard R64 Berdych 6-7(4) 6-2 7-6(3)
2006 ATP Masters Series Canada
Toronto, Canada Hard R16 Berdych 6-1 3-6 6-2
2006 ATP Masters Series Madrid
Spain Hard Q Berdych 6-3 7-6(6)
Seriously, I would back Berdych over Nadal on any surface other than clay. But especially at Monte Carlo, where the court doesn't play very fast, I don't see Berdych with good chances at all, unless the psychological edge is too big. Nadal's been playing very well and it's already been a good tournament for Berdych, considering how he arrived in Monte Carlo.
Just hope to see some needle out there, as I do enjoy tennis rivalries.