Would an Airport Express iron out my gateway's wifi issues if used as a stand-in?

I am currently lumbered with a low quality all-in-one router supplied by my ISP, (Alice/O2, Germany) the DECT phone is connected directly to it and we currently have 3 to 4 devices connected to its wifi broadcast, including an Airport Express, Apple TV, MacBook Pro and Compaq notebook.

The wifi broadcast is unreliable to say the least, the connection to my MacBook Pro has always been fine, but it regularly drops the connection to the AE and ATV. It's driving me crazy, watching a movie or trying to listen to music via the AE has just become tiresome, there are constant drop outs in connection.

My question is, could an Airport Express, if connected directly to this router with a CAT5 cable stand in for the router as a wifi hub?