Before this gets out of hand with trying to pry information from you...can you please expound a bit on what has changed from when everything worked to now when it does not?
There is no such thing as offering too much information. We're not mindreaders, but we are willing to help if you offer more information on the problem than what you have provided up until now.
Such as (but not limited to)
What version of WiFi are we talking about?
What old firewalls are involved since there are no "new" ones?
Why is your thought process for not using SP2?
Have you tried using the switch user mode offered in WinXP to see if the other profile can connect?
What are some of the names of the compenents being used?
Can the comp with the server even see the server at all when trying to connect with a client?
I think you get the picture at this point. Help us help you!