The vernacular is very confused these days. Republican and Democrat have nothing to do with political philosophy. Its the thoughts of the like minded people within them that terms the identity of the parties. For example, if we take parties as they were form, the Republicans are "anti-slavery" and the Democrats are "pro-slavery". Republicans are pro-centralized government, Democrats are pro-decentralized government. Republicans are for unconstitutional change, while Democrats are for strict constitutional adherence. All of these comments are taken straight out of the context of 1858-1864, during the civil war. The Republicans were for forcing new states to be either "slave" or "free", and the Democrats were for "popular sovereignty" (aka: let the states choose if they want to be slave or free).
Today, as well as 5 years ago, the Republican party is much different, as well as the Democrat party is different (though not much more). The Republicans AND the Democrats during the Bush years were both predominantly run by "Statists". Ala: They want central authority, have no regard with limited government, and believe that freedom is a gift from government. John McCain, Lindsey Graham, and a bunch of other Republicans fall into the "statist" definition. These "neo-statists" under GWB caused a LOT of problems for the United States and the rest of the world, especially in the developing world, by supporting policies that favored the foundation of strong central governments, and government controlled economies.
Neo-Conservatives (I am one) are opposed to tyrannical government, would not embrace tyrannical government (which was easily identified with GWB white house in the middle east, and central aisian dictators), and would be willing to reach out to protect democracies from neighboring tyrannical regimes. GWB and the republican congress during that time, did not differentiate between tyrannical or free societies when it gave support, it simply gave support to nations that were acting in the interests of the United States (without consideration to the actions of the source). As a Neo-Conservative, I believe that the United States must maintain a strong military in order to ensure global economic stability, which our own economy relies heavily upon. Neo-conservatives do not believe in simply striking the head off every dictator we come across, but it is vital that we not let WWII happen because the world is being run by a bunch of Neo-Marxists and Neville Chamberlains.
Todays Republican party is in a fight between "Conservatives" (of all flavors) and "Statists" (which the Left likes to call "Moderates"). The various Conservative factions have a solid rallying point, "The Constitution". The Democratic party today has nothing to do with the democratic party of the past (Kennedy and beyond). Todays Democrats are the Far Left, and their only common point is that they dislike the US for whatever reason and in varying degree's. This can be seen with leftists hecklers heckling Obama and Pelosi at well vetted Potemkin style town halls.
The Libertarians are also very closely related to Conservatives, and I would sleep soundly at night if the argument was between Conservative ideas and Libertarian ideas, but its not. Its between American ideas and European Marxist ideas. Fortunately, I think the statists are going to be run out of the Republican party, and going to be embraced by the left. Arlen Spectre and that loser from Florida, have shown their true colors. A couple more key Statist republicans to go, and there will be almost NO similarity between the Republican Party and the Democratic Party. Compare that to nearly 4-5 years ago when there was nearly no difference (at least in propaganda).