Hello Diego_82, welcome to the HPC forums, we will try to solve your problem.
I am a MobilePro 780 user too and I often sync over the network with a 10mbps PCMCIA card with modem capatilibities built in
(as if I need them
). Your card probably is just a straight LAN card.
If you want to know if it is working, put in the card, if a message box comes up with "Unknown card in socket 1 or 2", type in that box "NE2000.dll" to force load the NE2000 network driver, which should work in 98% of PC cards, including my D-link LAN\Winmodem combi card.
After that, if you want to make sure it works, just open Pocket IE and go to a site, if it finds it, you are in bussniess, if not, then wait a couple of minutes and try again.
Alternitively, Microsoft have some excellent tools in their "Windows CE 2.11 power toys", one of them is an IPConfig program, a more "Windowised" version of the Windows 9x/NT/2k/XP IPConfig program.
Download here:
http://www.microsoft.com/downloads/details.aspx?FamilyID=8b0788f7-bedc-4e3e-9c08-78b176152f44&DisplayLang=en
Also, follow the instructions on HPC factor for network syncrionsing if you haven't done so already:
http://www.hpcfactor.com/support/cesd/c/0012.asp
I hope this helps.