Port forwarding modem to airport

[geka]

y worst mistake? Having bought a D-link DSL-302G...
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I am running OS 10.3.8 on a powerbook and two Ibooks... I connect trough an old Airport Base and a D-link DSL-302G. *
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I never had port issues using my older modem.. even with the airport... but now with this D-link stuff... what a pain.
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Since I've installed the dsl 302G many apps... such as ichat, msn and may others won't work properly anymore... Ichat runs... but impossible to receive files or to run a video conference...
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I tried to fix that... doing a port forwarding in the modem... not the airport... but i can't do it..i get "501 method not implemented"
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So i tried to upload the new firmware... and again i got "501 method not implemented"
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Tried the d-link website... useless, especially if you got a mac.
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And my ISP... IInet doesn't do tech support for wireless networks...
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After a fair bit of googeling.. i tried to change the modem settings with the terminal... but didn't work... i'm not sure that I did it properly...
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What I'm looking for is a way to forward the ports from de DSL-302g to the airport so that they can be acsessible by both the powerbook and the ibooks...
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Please help...