Two IP Addresses on Same NIC

I've looked in Google Groups for my answer, to no avail. I hope
someone can help me. Please ask if I have left out something
important, because I don't want to waste your time writing a lot of
conditional diagnoses/prescriptions.

My hack:
Hewlett-Packard P3 desktop machine, no hardware modifications
Win98SE provided by HP, current with Microsoft patches
One network interface card (NIC), came with the machine,
HP EN1207D-TX 10/100 Family Adapter
LinkSys BEFW11S4 V.2 router (4-ports + WiFi-B), firmware 1.42.7
ZoneAlarm
WallWatcher (router log and analysis program)

Note in the winipcfg report below that the machine is in broadcast
mode. I sniff packets sometimes, when I want to know what is going out
from my machine.

The symptom -- When I do winipcfg (results below), I see two lines for
the NIC with the same MAC but two different, adjacent IP addresses. I
don't think a NIC should have more than one IP address, should it?.
The DHCP clients table from the router shows the same thing, two lines
with the same MAC but those IP addresses. The Wall Watcher logs show
that the NIC will call itself x.x.x.100 from boot-up for a couple of
hours, then spontaneously (?) begin calling itself x.x.x.101. If I
reboot, it comes up as x.x.x.100 again.

The problem -- None, actually. It's been doing this for months, in
fact, from the first time I checked. This hasn't caused any practical
problems that I know of, but I want to fix it before I add hardware or
software which can't deal with it.

Again, the winipcfg report follows my sig. (I've noticed the three
entries for the PPP adapter, with a mixture of "physical addresses."
The only time I have used this is through a USB cable to my old cell
phone (Verizon Mobile Office) for a few days till my cable was
installed. Maybe it is a symptom, too.)

Anybody got an idea whatsup here? TIA.

--Dook

++++++ BEGIN WINIPCFG +++++++++++
(This was immediately after a hard reset of the router, then starting
up the computer. Nothing else was on the network.)

Windows 98 IP Configuration

Host Name . . . . . . . . . : [deleted by Dook]
DNS Servers . . . . . . . . : 216.148.227.68
204.127.202.4
Node Type . . . . . . . . . : Broadcast
NetBIOS Scope ID. . . . . . :
IP Routing Enabled. . . . . : No
WINS Proxy Enabled. . . . . : No
NetBIOS Resolution Uses DNS : No

Ethernet adapter :

Description . . . . . . . . : PPP Adapter.
Physical Address. . . . . . : 44-45-53-54-00-00
DHCP Enabled. . . . . . . . : Yes
IP Address. . . . . . . . . : 0.0.0.0
Subnet Mask . . . . . . . . : 0.0.0.0
Default Gateway . . . . . . :
DHCP Server . . . . . . . . : 255.255.255.255
Primary WINS Server . . . . :
Secondary WINS Server . . . :
Lease Obtained. . . . . . . :
Lease Expires . . . . . . . :

Ethernet adapter :

Description . . . . . . . . : PPP Adapter.
Physical Address. . . . . . : 44-45-53-54-00-00
DHCP Enabled. . . . . . . . : Yes
IP Address. . . . . . . . . : 0.0.0.0
Subnet Mask . . . . . . . . : 0.0.0.0
Default Gateway . . . . . . :
DHCP Server . . . . . . . . : 255.255.255.255
Primary WINS Server . . . . :
Secondary WINS Server . . . :
Lease Obtained. . . . . . . :
Lease Expires . . . . . . . :

Ethernet adapter :

Description . . . . . . . . : PPP Adapter.
Physical Address. . . . . . : 44-45-53-54-00-01
DHCP Enabled. . . . . . . . : Yes
IP Address. . . . . . . . . : 0.0.0.0
Subnet Mask . . . . . . . . : 0.0.0.0
Default Gateway . . . . . . :
DHCP Server . . . . . . . . : 255.255.255.255
Primary WINS Server . . . . :
Secondary WINS Server . . . :
Lease Obtained. . . . . . . :
Lease Expires . . . . . . . :

Ethernet adapter :

Description . . . . . . . . : HP EN1207D-TX 10/100 Family Adapter
Physical Address. . . . . . : [MAC deleted by Dook, same as below]
DHCP Enabled. . . . . . . . : Yes
IP Address. . . . . . . . . : 192.168.1.100
Subnet Mask . . . . . . . . : 255.255.255.0
Default Gateway . . . . . . : 192.168.1.1
DHCP Server . . . . . . . . : 192.168.1.1
Primary WINS Server . . . . :
Secondary WINS Server . . . :
Lease Obtained. . . . . . . : 11 05 03 3:05:36 PM
Lease Expires . . . . . . . : 11 06 03 3:05:36 PM

Ethernet adapter :

Description . . . . . . . . : HP EN1207D-TX 10/100 Family Adapter
Physical Address. . . . . . : [MAC deleted by Dook, same as above]
DHCP Enabled. . . . . . . . : Yes
IP Address. . . . . . . . . : 192.168.1.101
Subnet Mask . . . . . . . . : 255.255.255.0
Default Gateway . . . . . . : 192.168.1.1
DHCP Server . . . . . . . . : 192.168.1.1
Primary WINS Server . . . . :
Secondary WINS Server . . . :
Lease Obtained. . . . . . . : 11 05 03 3:05:36 PM
Lease Expires . . . . . . . : 11 06 03 3:05:36 PM

++++++++ END WINIPCFG +++++++++++++++