The best way to do this is to use DFS.
Basically you set up what is known is a dfs name space, for example, \\yourdomainname.local\DFS
\Home.
You then create two folder replicas, one for each site.
You then use DFS replication to manage the updates and replication of the data between the two sites and you use DFS to host the virtual name.
What happens is when a client navigates to their profile name, which has to be \\yourdomainname.local\dfs
\profile etc, they will automatically be redirected to the closest replica.
DFS is pretty easy to setup, and it works a lot better with R2, but works ok with standard 2003 server.
Have a read of this and see if it helps
http://technet.microsoft.com/en-us/library/cc778480.aspxSteve