|Start > Programs > Accessories > Communications > Internet Connection Wizard|
Make sure you select the LAN option, then click next all the way through each dialog and leave the rest as default. Then click Finish and launch IE or Firefox to see if it loads.
iMac G5 1.8GHz "Hero" PowerPC
2 x 1GB DDR PC3200 SDRAM
160GB WDC WD1600JD-40GBB2
Mac OS X Leopard Version 10.5.8