Even if true, I fail to see what the problem is.
The Commander in Chief would be derelict in duty if he did not think ahead and start planning tactics long before you go to Congress with firm and final plans.
The problem, according to the memo's floggers, is that it wasn't merely strategerizing in advance of a possible war. The memo alleges that facts and intelligence were manipulated around the general policy goal of removing Saddam in order to make a case for war. It also alleges that there were attempts to provoke Saddam into doing something to give us an excuse to start shooting. The third big allegation is that there was no thought given to post-conquest planning.
If this stuff turned out to be true, it's the worst thing that could possibly happen for our Iraq policy, since it would show the moonbats were (shudder) right.
Big problem is that Blair's office hasn't to this point refuted the accuracy of the memo. Dunno why they'd do that if it IS BS.