The term is generally used to describe a faction of conservatism normally associated with Buchananites, anti-immigration people and the sort. Some argue that they are anti-Jewish as well, though there are also Jews who describe themselves as "paleos."
By contrast, David Frum seems to think that a "paleo" is anything and everything that does not agree with him whether the label is accurate or not.
In a nutshell - Paleoconservatism is a name used to distinguish the traditional conservative movement (and those who adhere to it today) that existed before a group of Trotskyites, liberals and Democrats claimed they were "conservative" and moved into the Republican party and become dominant. Basically the neocon's accept FDR's New Deal socialism as well as Johnson's Great Society as good ideas (just managed poorly) i.e. they are for a strong central government and the welfare state. On foreign policy they go far beyond national defense to the point where they are down right aggressive, belligerent even. Paleocons see this stance as dangerous to the national health and world peace.
Neocons have been trying to personify paleoconservatism as the very embodiment of a racist pre-civil rights US. This tar brush is designed to paint their opposition's ideas of all kinds - foreign and domestic as beyond the pale. Basically this fight is about maintaining the position of power the neo's have achieved. Since some of the paleos aren't suffering the slander in silence the fight is getting nasty.
Click here to hear it from the Paleoconservative's mouth.