Have you set the wireless connection to be controlled by windoze?
If so, untick it so that the Intel software is used, otherwise try ticking it so windows controls it.
Try setting static IP config, see if you can ping the router.
Also check the advanced settings of XP's firewall as even though the main screen can say it is turned off, you have to go to the advanced settings and untick all the connections. I know it shouldn't affect DHCP but you never know with microsoft
