10/100 might be displayed... but it might be to old to have it. You can get a card, which fits the slots your mobo has... But I would think it doesn't have it onboard.
Found this...
IBM Aptiva C8H
(250-0462) Specifications Faxback Doc. # 38232
Design:...........................................................Minitower
Processor:..................................................166 MHz Pentium
w/ MMX technology
Speed (Int/Ext):.................................................166/66 MHz
Slots(ISA/PCI):.......................................................(5/1)
Shared Bays (Total/Avail):............................................(6/3)
Memory (Std/Max):...............................................(16MB/64MB)
Open Memory Sockets:.................................................1 DIMM
L2 Cache (Int/Ext/Max):..................................(32KB/256KB/512KB)
Hard Drive:...........................................................3.1GB
Diskette Drive:......................................................1.44MB
Power Supply:..........................................................145W
Video Chip:......................................................ATI 264GTB
3D Graphics:............................................................Yes
Video DRAM (Std/Max):.............................................(2MB/2MB)
Max Res:........................................................1280 x 1024
Max Colors:.............................................................16M
Ports:..............................................VGA, Parallel, 2 Serial
..Joystick, PS/2 Keyboard, PS/2 Mouse
Modem Support:
Data/Fax/Voice/Speaker Phone
Data:............................................................33.6Kbps
Fax (Send/Receive):...........................................(14.4/14.4)
CD-ROM:.................................................................16X
Audio Card
Wavetable Audio:......................................................Yes
3D Sound:.............................................................Yes
Video Phone Ready:......................................................Yes
Speakers:...............................................................Yes
Microphone:.............................................................Yes
MPEG:.............................................................SW MPEG-1
Home Automation:........................................................Yes