SqlDependency
http://msdn2.microsoft.com/en-us/library/dzf68kas.aspx
There is a cool new feature in .net 2.0 it is called SqlDependency it fires an event on sql result change. It allows a kind of asynchronous triggers and is probably the best choice to monitor foreign applications databasess for changes.
Only gotcha is you have to enable service broker on database being monitored.
Of course works only on sql server 2005.
I expect it will help in earning some bucks 
