Being able to ping the IP address sucsessfully is a good start as Rob pointed out, here are a couple of other things to check once you have tried that.
Are you using ETH driver in RSLinx or are you using ETHIP Driver?
Here is something to try if you have not already.
Go into RSLinx and look to see if you have a ETH driver set up already. (If you are connecting to a 5/05 successfully already,then I will bet that you do have this driver set up already in RSLinx)
If you do High Light it and press configure driver and see if the IP address of the Processor you are trying to connect to is shown in the configuration.
If not you will need to add this IP address manually.
If you do not have a ETH driver, then make a new ETH driver,
Then press Configure Driver and MANUALLY enter the IP address of the processor you want to connect to.
Say ok or accept or what ever it ask for to save this driver and then close that dialog box but keep RSLinx up and running.
Now go to RSWho and expand your ETH Driver and see if you can see the backplane and the 00 processor in RSLinx.
If you can see the backplane and processor here then you are on the right path.
Now go to your Logix5000 software select communications > Who Active Go ON LINE, once this comes up select the ETH Driver and expand it, then navigate to the backplane and expand that, you should see your processor now, highlight it and say go online.
(You are using Logix5000 software to try to connect to this Control Logix Processor right?? Logix500 will not work, sounds obvious enough but you never know.)
Give this a shot and see if you can connect, if not supply more info and possibly screen shots and someone will help walk you though it.
BCS