k in theory, i believe the modem from izzipro must have NAT enable(routing function)

but its confusing when u set pppoe on ur router, wherelse this should be on the modem itself, like what was asked from karhoe. if the pppoe dialing is from the modem, then u set ur wan setting in the di624 as dynamic

and its very unusual for ur modem to have such a weird IP, 192.198.*.*??

k basically the MTU is Maximum Transfer Unit, the lower it goes, the slower your comp goes, u only change this when u cannot access certain websites or some application like msn or Outlook not working, then lower u change it, the slower it goes,defaull is 1400 to 1500, do not go lower than 900

basically if the modem u got there is half bridge or fully bridge, u can do the dialing(PPPoE) from the router, that means the modem is a dumb modem, acts only as a modem, no routing or NAT functions, mean u dont really need to change the IP to suit ur modem, but if ur modem is bridged, where got IP?

thats why i said its confusing, sorry for saying that coz u never provide details description on ur topology and IPs ...