[Salocin]

Beren's fea was sent to Mandos.

I do not beleive it was. As I remember it, Beren's fea left the circle of Arda like that of all men and went to a fate known only to Eru. Luthien died of grief soon after Beren's death. In the halls of Mandos, Luthien sang a beautifully sad song to Mandos which touched him so much that he interceded for her to Eru to change Beren's fate. Eru headed the plea and granted Luthien the choice to bring Beren back and live with him in Middle Earth for a while, but in exchange to become mortal and follow the fate of men allong with Beren. She chose this fate and Beren was brought beck to Arda where he married her. They lived on an isulated island in the middle of a stream untill they both passed away again. The isulation was partly voluntary and partly manditory because Beren was the only being in all of Arda, including the Valar, who knew the fate of men after death.

When men die they go to a place thats near the place where the elves die (in mandos) but from there it can go three different ways.

I do not remember there being a reference to any man being aloud in the imortal lands for any amount of time including Beren. I am pretty sure the left Arda imedeatly after dieing.

From the Silmarillion, I learnt that the hall of mandos was used for housing the fea of the eldar and perhaps the dwarves'

I do not think dwarves went to the Hall of Mandos either. I am pretty sure Gimli is the only dwarf to set foot in the undieing lands.

There is the question of the Paths of the Dead episode, in which the men who had reneged on their vow to Isildur had their fëa trapped in Middle Earth for 3000 years until they eventually made good on their obligation by coming to Aragorn's aid.

I believe it was their own oaths that kept them trapped in their graves till they fufilled them. It sure is a scarry punishment for breaking a promise!