Hello padrefrancisco, welcome to androidforums!
I can't seem to find anything on that modem, is that a USB dialup modem by chance?
If so, I'm not so sure of a way to get it to work. I would think that the Android tablet would need some sort of PPP software to initiate the connection.... and I don't know of any.
Now, if you are able to get the modem working with XP, is there any chance that the XP machine has a Wireless LAN adapter? If so, you might be able to do "Internet Connection Sharing". I used to do it with Vista, so I'm not sure the exact steps with XP... but I was able to share my dial up line over an ad-hoc wireless network to my ipod
If you don't have a WLAN adapter, you might want to look into a USB dongle ... I have a Belkin that I use from time to time that works pretty well.
Hope that helps, and welcome to the site!
-9to5