Take a look at SymmetricDS.
1) SymmetricDS works with SQL Server.
2) Supports mapping records from table A to table B.
3) Comes in open source or professional versions.
Open Source:
SymmetricDS.org
Professional
JumpMind.com
4) Uses triggers, and some other stuff.
There is a free 30 day SymmetricDS Pro demo at JumpMind.com.