Is there no cheap way (besides serial) that i can have a network on the A4000 ?
The XSurf also has a traditional RJ-45 plug, so that's an option.
The most cost-effective means of getting online, though, is probably through a USB->Ethernet adapter. A USB card is a larger initial investment, but it opens the door to so many other (cheap) peripherals that it pays for itself very quickly.