Can someone PLEASE help me do this? It's been 3 days and I'd like to revert back to the old settings since one of my laptops is no longer connecting, but I can't.
Please help.
Pretty much what jl449 said. Add netmask as 255.255.255.0 too and it's right click on Local Area Connection 1 or 2, or whatever one is active (doesn't have a red x mark over it).
If you still can't manage it search on Google for: configure fixed ip settings windows xp, or something similar. There are countless of guides that contain images. This is a Windows operation. It has nothing to do with DD-WRT or D-Link or routers, so it is kind of pointless to wait 3 days for an answer on a forum dedicated to these when you can find the solution within minutes on Google.
Also, weird with the laptop no longer connecting though. I doubt it's because of DD-WRT. Have you modified any of the settings? Set the wireless mode to mixed, set wireless security to WPA2 Personal with AES.