Will i have trouble connecting my PS3 to a linksys WRT54G WiFi router if my PSP cannot find an access point?

May be...

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I don't believe that linksys routers support AOSS, WEP should be the encryption best for portable devices like a PSP. Try using normal wireless setup instead of AOSS and if the PSP associates with the AP but doesn't get a IP Address, try setting a static IP address on the PSP instead of having it get the address through DHCP. The Secure Easy Setup button is not the same as AOSS sadly so you could be associating with it incorrectly. Also the PS3 should connect fine, If you buy one and neither of them connect, it could be a AP issue. In my references I gave links to some Connection setup guides for the PSP, they might help you.

hmmm there may be an issue with your PSP's wifi, I have the same router and am able to connect both PSP SLim and PS3