[MickMcGeough]

First, dual-band means that the router operates on more than one frequency. Wireless G is 2.4Ghz, but Wireless N can be 2.4 or 5Ghz. You only need dual band if you want the 5Ghz band for your wireless N devices (assuming they support it - many don't).

In theory, having an 802.11n/g router running in backwards compatibility mode with 802.11g will have no impact on performance. In practice (at least with my D-Link router), going to 802.11n only mode had a very small performance increase.

Two very important points about 802.11n:

1. Make sure that your router supports both 20Mhz and 40Mhz modes. My 802.11n devices on 40Mhz have significantly better throughput than they do on 802.11n 20Mhz.

2. Don't listen to marketing jargon on 802.11n device throughput. Nothing can sustain 300mpbs (at least nothing you'll find at Best Buy or whatever) although they will all claim it. I've gone through 3 802.11n routers and about 5 802.11n devices and the fastest configuration I've found couldn't sustain more than 50mbps in my area (which is pretty good - fast enough to stream uncompressed HD video and 5.1 audio). On a low-end D-Link 802.11n router, I couldn't get higher than 25mbps. A good 802.11g router would probably have been better.

I don't know about PS3 802.11n support, or why setting up a bridge would allow the PS3 to utilize N...

Finally, if the PS3 can support 5Ghz 802.11n, make sure you do get a dual band router with 5Ghz support. The 2.4Ghz is ridiculously saturated with other wireless devices, wireless phones, microwaves, you name it. If you live in the city you will have a hard time getting very high performance out of a 2.4Ghz 802.11n network.

ETA: Sorry, didn't see you were hardwiring the PS3. My points still stand. If you can, get 5Ghz 802.11n support on your media server and plug your PS3 in directly to the 802.11n 5Ghz router.