Urgent Situation

Hi Guys the situation may is quite intresting here

I have two system at my home one is the Dell laptop that supports wireless connection. and second is Desktop (desktop has wired conection to internet).

since my laptop is a wireless one I was using the wireless internet connection
of my brother (next door).

around 2 weeks back I Installed SP2 for XP and it was working fine... but recently I am not able to connect to wireless internet on my laptop
I was getting limited or no conectivity .
The following things i did to rectify this.

switched off and on router again
removed SP2
re-installed XP with SP1
reinstalled drivers for wireless card (intel pro wireless 2200)
ipconfig / release / renew
winsock fix
(In the same order I specified)
but still i am not able to surf wireless
however if i remove the internet cable from my deskop system and put it into my laptop then internet is working fine.

the point to ne noted here is, there are two different networks here
one is mine (wired one) and one is my brother's (wireless).
is it a problem to keep two diff network?

PLEASE HELP ME FOR THIS I want to USE wireless connection again

THANKS
ROHIT