Yeah basically what Arvindian said... except from those two I would go with the 825. I like and actually use the dual band though. And it does dual band without hiccup which was one of my main concerns when I purchased my router if you don't need it though go with the regular 655 it performs just as well regardless of what the box says for end users. 825 model probably comes standard with a bit better user interface given D-links history of user interface upgrades but both are updateable to the current interface design.
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Cable modem or adsl? If cable no it doesn't matter. Certain adsl modems may require bridging of connections easily done but you may have to call whoever your service provider is depending on what you have to do there it may require you to port forward on the router/open nat. This is also easy to do on these routers and a quick google search will help you through all those settings as well as calling D-Link directly. Hope that helps you a bit mate. Have fun with which ever router you choose.
it looks like both are pretty equal but according to the chart given the only difference they note is that the 825 has 5ghz option that allows for HD Streaming of video(dual bands).
if this is just for the ps3 then either should be fine IMO. Since the PS3 only sports wireless b/g and not n.
unless your wired which still wouldn't matter since both routers sport a Gigabit port and the PS3 does have one of those.
if your going to go wired please note that you may want to use Cat5e or a Cat6 cable.
the differences is minimal cat6 only allows you to be "future-proof" for the time being.
*as a note these are only my opinions and any man can be wrong including this guy.