From what i read about 64 bit computing at its current state, the best way to use it is to emulate 2 processors, Slack has no support for 64 bit processing and most OS are "faking" support as well there is no call for it just yet, but intel are about to release a prosuction 64 bit processor so i think now we will see a bit more in this realm.
Note: there is a project called SLAMD64 which is slackware 64 but it is unoficial
