Wireless timing out on my MBP with WPA security

I changed from an open wireless connection to a WPA security connection, and ever since my macbook pro (core2 intel) just drops connection and times out after maybe 10-15 minutes of surfing the web. It never did this before when there was no security enabled on my netgear router. I am running 10.4.5
Any suggestions?

Thanks,
Alex

If it hangs on "looking up google.com..." I just turn off the airport, then back on, and it works again. So annoying.