The plan is that we have a simple webinterface (PHP-based) where we enter the receiver, the amount, the username (will correspond to the name of the wallet file) and the wallet password. The script would then send the data to bitcoin-qt (or whatever we use) which will then execute the transaction. Also, it should be possible to view the amount of BTC that each wallet has (After entering the password of course).
So, you basically want to create a web wallet service? It's a pretty easy thing to do by using bitcoind's json-rpc connection. Do be carefull about your security tough!
Offcourse, bitcoind will need to be running as a daemon, and only one wallet file can be opened at a time.