Any switch will do, just make sure its not a hub (which is very similar to switch, but works a lot differently).
This is the same switch I use
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Its actually very good for so cheap. You can also pick these same ones up at Wal-Mart or Best Buy for the same price, sometimes less.
And as I said before, length on the cable really makes no difference. The data travels so fast, the amount of 'extra' lag you would get would be unnoticeable. Only way you would see some noticeable lag is if you had some really long cable (like 500ft or more). And even that be very minimal. I am not why or how foolness got a extra 15 seconds due to adding 20ft of cable, but I can guarantee you it not because of the length of the cord. Something else is causing the extra lag.
Just stick with the switch, which should get you some decent (manageable) lag time. Make sure the Ethernet switch is between your router and PS3.
Example.
Modem -----> Router -----> Lag switch ---> Ethernet switch ------> PS3
Obviously the best possible way to do it is by sticking the lag switch between the router and modem... but if you cannot do that, this will be the next best thing.