Your connecivity is good then.
I could give you detailed instructions about how to clean out crap in your HOSTS file, and Winsock server stacks, but fortunately for both of use this had been done:
1. Repair on the bad notebook client your registry stacks for Winsock:
2. Under IE, Tools, Internet Options, delete all "Temporary Internet Files"
3. Run Spybot:
4. Run AdAware:
4. Under "My Computer", double click, then right-click your drive C. Do the disk cleanup.
I am not kidding that you need to do all of these steps. I honestly do not think you have a trojan or malware on your client workstation. But humour me, lets make certain. The disk cleanup and removal of temp files has to do with problems under Windows with negative DNS Caching. The reboot asked for is similar. If you have failed DNS requests repeatedly under XP it may just fail a subsequent request even if it could succeed.
Final note: I have on a day-to-day basis both wired and wireless clients in my home. Anytime I play with the router I disconnect everyone but me (wired). I reset the router to manufacturer's defaults. I hold down the reset button for nearly one minute. I wait until the red dia light comes one, everything flashes, and the red diag light goes off.
I unplug it for 1 minute. I plug it back in and when it appears stable, put back all of my settings.
I then unplug it for 1 minute. And plug it back in.
I would not risk using a wireless client to change the router settings.
It sounds like what you need is to change port forwarding assignments. If you explain what ports need to be opened, I think it could be done with a combination of freeware 3rd party utilites and uPnP.
Reboot.