Computer make & model?
Operating system?
Model name of wireless network adapter?
Model name of wireless router?

"I recently had it re-installed."
Reinstalled what? Adapter, driver, Windows XP, other?

Update router firmware to latest version.

If the wireless adapter is internal and was pre-installed by the computer mfg, install the latest adapter driver from your computer mfg.

Otherwise, install the latest wireless network adapter DRIVER from networ adapter mfg. DO NOT use the driver that Windows XP installation disk provides. DO NOT use the driver that Windows Update provides.

Some wireless adapters have their own firmware (usually PCMCIA/PC-card versions). If this is the case you might need to update the card's firmware.