Vista won't share internet with XP

Here's my situation: I have a Vista home premium machine hooked up via
USB to a cable modem. I have an XP machine networked to the vista
machine via a crossover cable (UTP?) via the ethernet cards.
Until recently, I was able to share files between machines and the XP
was able to use Vista's internet connection. Then, something happened. I
don't know if one of the machines updated something or what, but I lost
the connection entirely. After fiddling around with various settings,
both machines can now see each other and I can move files, but the XP
machine no longer has the internet connection from vista. XP tells me
that the host did not assign it an IP address. All the sharing settings
on vista are turned on, and everything had worked fine before. I tried
all the various repair options, but it just keeps telling me there is
limited connectivity. I've reset the modem and adaptor multiple times,
rebooted both machines and nothing seems to work.
Does anyone have any ideas why the machines can see each other on the
network but XP can't use Vista's Internet connection anymore?

I'm a newbie when it comes to networking, so please explain any
solutions in detail. Thanks!
Todd


--
tshryock