Environment:
Windows Server 2003 computer name: queen
Local Users: Administrator, John, Simon
To simplify, both John and Simon are members of Local Administrators group.
SQL Server 2005 installed
Three databases: AdventureWorks (case sensitive), aData, and bData
A table dbo.DOCS in AdventureWorks is shown:

Create a Merge Publication, Add Filter as shown below:

Create a subscription and make user the Merge Agent security use QUEEN\Administrator.

You can create another subscription for bData database with Merge Agent security: QUEEN\John. You will find the records with QUEEN\John are replicated.
Interesting observation:
Insert a record into the Subscription:

Same thing happens for bData.

I didn't create real scenario to use HOST_NAME() (computer name). You should have a table with a computername column.