Many times while i try to download something, my connection hangs without an apparent reason. I lose access with the internet completely, icluding the built-in web interface of the router! This doesn't happen everytime but at random intervals.
Do you have a PC or another ethernet device you can use for testing?
Two possibilities jump out at me:
1) The ADSL modem is crashing.
2) Your PCMCIA network card dies.
Without some other device you can use to test for those two possibilities, I'm not sure what to tell ya.
Do you lose link light on the ADSL modem when this happens?
Should i spend some time to forward only the ports which are required by p2p apps and such? Currently i'm running it at "demilitarized zone" mode. (forwards all ports) Is this dangerous in an Amiga setup?
It's probably not "dangerous" for an Amiga setup to be in the DMZ, as not too many things exploit one. ;-) Really, though, at least for testing, put yourself in the NAT, and just let the ADSL modem filter all the incoming crap that heads your way. One less variable to worry about.