Read the memo yourself here. Note that the information contained therein is quite basic and has no information that the President or his National Security Advisor would not have already known: al-Qaeda is an extremist Muslim terrorist group of significant size, influence and resources given refuge in Afghanistan. Considering that Clinton launched missile strikes at Afghanistan in 1999, that Clinton had twice refused Sudanese offers to extradite bin Laden and that the Khobar Towers and Kenya/Tanzania embassy bombings had long since taken place, Clarke's memo held little information on al-Qaeda that was not already known when the Bush Administration was engaged in transition in late 2000.
Clarke wanted a principals-level meeting on this issue. Rice discussed this at a higher level because she felt that the Clinton Administration's policies toward al-Qaeda had run out of gas. More information on the memo, which was declassified before Dr. Rice testified to the 9-11 Commission, is here. Note this exchange at the Commission hearings between former Senator Slade Gorton and Clarke in discussing this memo:
SLADE GORTON, Commission member: Now, since my yellow light is on, at this point my final question will be this: Assuming that the recommendations that you made on January 25th of 2001, based on Delenda, based on Blue Sky, including aid to the Northern Alliance, which had been an agenda item at this point for two and a half years without any action, assuming that there had been more Predator reconnaissance missions, assuming that that had all been adopted say on January 26th, year 2001, is there the remotest chance that it would have prevented 9/11?
GORTON: It just would have allowed our response, after 9/11, to be perhaps a little bit faster?
CLARKE: Well, the response would have begun before 9/11.
GORTON: Yes, but there was no recommendation, on your part or anyone else's part, that we declare war and attempt to invade Afghanistan prior to 9/11?
CLARKE: That's right.
The media will make this a tempest in a teapot, but just remember that Clarke himself said that if everything in the memo had been implemented (and there's a dearth of concrete plans in there), 9-11 would not have been prevented.
For some background and refreshers, see our posts here, here, here, here, and here.