My Set up is as follows
BT Home Hub Mk1 - TKIP Encrypt.)
Old Compaq - Xp Home with Belkin Wirless PCMCIA Card 802.3/g - No on board Wireless - Upgrade to XP3. No probs at all.
Clone (AJP Now AZUS) - XP Home on Board Wireless Realtec 802.3/g Wireless - Wireless would not work - connection established to router but limited/ no connectivity. went back to Backups. XP2 only works fine.
New (5 Weeks ago ) Dell Vostro 1310 using in built wireless card 802.3 G - XP pro SP3. A day of misery, now working by temporarly allowing Windows Zero Config service and getting Wondows XP PRO to repair connection. WZC then disabled. use Run, Msconfig to disable/enable/disable the service. Microsoft do a Reg fix to stop you being pestered to upgrade to XP3
In short impossible to predict behaviour .
CAT III