hello my friend has had a very bad experience even though I told him Ubuntu would not run very well on his computer or if at all, his computer is an older one only 512 k mem and a athlon 3200+ now I have looked for him and found Xubuntu looks to be better for him but I need to know he only has a T Mobile zte 620 VSB mobile dongle and he thinks it has been configured to run only in XP does Xubuntu come with a usb switcher so his internet dongle will work

Hey mate, i live in Australia, and i am in a similar situation where i have to use mobile dongles. I use one by a provider which only supports "Windows and Mac OsX" Not Linux. I have a mac with both them operating systems on it, and when i plugged the dongle in to them for the first time it installed some crappy software needed to access the internet. On Linux it will not install any software. Network manager however does a great job at detecting it and connecting to it. I like kde, but i find kde's network manager applet horrible with it though, so i always use gnomes, as it has always worked. As a side note though, i'm trying out kde 4.7 on opensuse and i don't know if kde have made the change or if opensuse have made edits, but i actually can connect with kde networkmanager applet in opensuse 12.1. That's irreverent though since your mate'll be using xfce. I'm pretty sure Ubuntu puts gnomes applet for network manager in xfce, so i think he'll be fine. Use a live cd for Xubuntu and see if it works.

Most USB dongles work under Linux. Zte's seem to be supported well under Linux (i have a Zte 110 and worked out of the box with network-manager).

Network manager either works either doesnt with them. Its a matter of luck.

The best solution i have seen so far is sakis3g (http://www.sakis3g.org/#downloading) - a standalone script that switches, configures and connects USB 3g modems. Its very light (300kb) and no dependencies. It uses the available usb-modeswitch, ppp, vwdial though.
The very good thing about it is that it can even use modems that were not configured by the kernel or network-manager as modems.