PC sees router, but can't get to internet

[Dan <dan27649@xxxxxxxxx>]

My son brought home a WinXP-Pro PC from a friend of his with which he wants
to load SP2 on, as well as all of the latest updates.  It sees the router;
we can type in the address of the router and the router menu comes up.  But
we can't get past that point.  Pinging to a known outside address fails.

One thing that seems odd to me is that the IP address assigned to this PC is
192.168.0.101.  The range I've specified on the router 192.168.0.100 through
192.168.0.199.  As I already have four other devices on the router, I would
have thought that 101 would already be allocated to one of those devices.  I
failed to check this as it was 1:30 in the morning.  I did try to see if I
could change the IP address of this computer, but no luck finding anything.

FWIW, no problems with the other devices on the router reaching the
internet.

Any ideas?

TIA,
Dan