Programming a solution to know when a Bitcoin Address has stored a target amount
A rough solution:

If the account is in your wallet, you can use:

bitcoind getreceivedbyaddress "ADDRESS"

to get the amount of bitcoins received by ADDRESS. You can put that line inside an infinite loop. You could create a shell program which stores the result in a variable every 30 seconds (using sleep) and compare it to the previous value. If you subtract the values and find a difference above a threshold you can make the script alert you. 

I can be more specific if you tell me your preferences (Python, Linux shell...)