Ok, this is going to be a long reply because there could be a whole host of issues
(1) I assume you have the model that includes the network port.
(2) I assume you have a DHCP router (your computer IP is 192.168.x.x)
If that is the case here are a few things that could be wrong.
What IP did you assign the printer, make sure is not x.x.x.1 or x.x.x.255?
What Subnet Mask did you assign, 255.255.255?
What Default Gateway did you assign? 192.168.1.1?
For the above answers, the SN and Gateway should be the same as your computer, to check go start>run>cmd>ipconfig
Can you ping the IP address assigned to your printer from your computer?
If you have checked everything and cannot ping the IP then there was a problem in setup.
How did you set the IP, via the USB port of via printer? If you know how to add network printers I would reccomend setting the IP via the printer else you will need to use the CD.
Here is how you add the network printer via M$ - its a tad technical so beware
http://support.microsoft.com/kb/314073/
If you can give me some more information I can troubleshoot further. I have a feeling you tried setting everything up with the printer connected via the network cable in which case the printer is still using the default IP.
A few other things that might be wrong, your router might have MAC filtering, if it does turn it off (you would have had to run it on to begin with) or add the printers MAC to the list.
Check your routers DHCP scope, set the printer IP to one that is not in the scope, example
My computer IP 192.168.168.100 SN 255.255.255.0 (class C) dg 192.168.168.1, I have the DHCP scope set to 192.168.168.100 - 150 (I do that mostly for security as I have a dedicated computer scanning those IP to ensure no one has hacked my wireless WPA and to ensure there is no intruder. Because my range is 100-150 I setup network devices in the 50-100 range.
Hope that Helps - man I was just looking over the tech sheet for it, 6 ink cartridges, you must be rich to afford to replace those - geesh.
Also it might be easier to uninstall the HP software and then set the printer up manually as a network printer. PM me and I will send you more detailed instructions.
MYK