Captive Portal Setup

When someone logs into my Wi-Fi network I would like them to be redirected to my specific website.

If they try to access another website such as google.co.uk - I would like them to be redirected back to my specific website.

I've tried to achieve this with DD-WRT and "Hotspot System" but my lack of technical knowledge is proving a stumbling block.

Does anyone have any experience of either "Hotspot System" or "Sputnik", "Wifidog", "Chillispot" etc?

Looking forward to your replies.