This requires a multi-master replication model, which SharePoint doesn’t support.

Do you know any third party tool which can achieve this.

Otherwise is it possible to have two stand alone sites  be an exact replica of each other using some sort of Database Repliaction.

I don’t know of a third-party tool that will do this.

AS for a replica, no – I don’t think you should attempt this. SharePoint isn’t setup for replication – even if you use SQL DB replication with log shipping. There is no method that I know of to do a conflict resolution at the content layer when the sites  get out of synch. I would strongly suggest a different design.

iOra sells a tool that will maintain two SharePoint sites  in synch
(two way replication). It does this by reading changes on one
server, sending compressed changes over the WAN, and applying the
same changes to the other server through web services calls. This
means that the two sites have the same content, but they are not
identical at the database level (eg the same item will have
different GUIDs in the two environments).

It does this for WSS/SPS 2003 and also supports MOSS 2007 within
obvious limits for a beta environment.

What you could do here is use Site-linked GPOs to launch scripts or set IE variables to prepare/configure the users shell for whichever office they are in at that particular moment.

more of a windows infrastructure issue.