Ethtool bug or driver bug or faulty built-in NIC ?

Question

First the hardware particulars -
- The laptop in question is an Acer Aspire 5050 with an AMD x86-64 Turion cpu
- There is an on-board SATA chip (unused), which throws up some very odd errors but except on slackware distros, seems to do no harm. {It cannot be disabled in the bios either thanks to Acers craptastic bioses.}
- It has an IDE WD 120gb hard drive and an ATI 200M video chipset (xorg IDs it as an 1100 IGP/465 chip)
- The NIC in question is: eth0: RealTek RTL8139 at 0xf8848c00, IRQ 18; eth0: Identified 8139 chip type 'RTL-8100B/8139D'.
- Ethtool reports this in querying the Nic in question:
Settings for eth0:
Supported ports: [ TP MII ]
Supported link modes: 10baseT/Half 10baseT/Full
100baseT/Half 100baseT/Full
Supports auto-negotiation: Yes
Advertised link modes: 10baseT/Half 10baseT/Full
100baseT/Half 100baseT/Full
Advertised auto-negotiation: No
Speed: 10Mb/s
Duplex: Half
Port: MII
PHYAD: 32
Transceiver: internal
Auto-negotiation: off
Supports Wake-on: pumbg
Wake-on: d
Current message level: 0x00000007 (7)
Link detected: no
Now to the issue at hand
This is not so much a problem as it is an annoyance really. For whatever reason, on several distros that I have investigated, my on-board nic is incapable of being used at the 100mbit setting it is capable of using.
Typically when I first boot a distro, the nic is detected and will work fine, however it runs at half-duplex and on 10mb/s. It is capable of full duplex mode & 100mb/s.
I did alot of research about how I could enable full duplex and 100mb/s modes. I found ethtool to be the answer, or so I thought. However, when ever I've used ethtool, it will set full duplex mode correctly but if I tell it to set the card to use 100mb/s mode, the link itself will not stay up. It insists there is no link detected and restarting the network connection does nothing, as the card never receives an IP address from my router. As soon as I revert the card to 10mb/s and restart the network connection, I receive an IP as expected.
To date, after having googled my brains out, I have not found any solution to this little dilemma. I have asked on a different forum a similar question but the few people there could not give any answers.  The only real answer I got was to swap out NICs (a somewhat useless suggestion as it is built-in). I hoped that posting here, perhaps someone with a similar NIC could offer any insight into this issue.  Failing that, could someone tell me if I should report this as a bug to some developer perhaps (Ethtools' dev?).
I will provide any other information possible on-demand to any who may have insight. For now, I've posted as much as I could think of to help shed light on this.
MS

Answer 1

There are two Realtek modules, 8139cp and 8139too. See which one is active, kill it, and try the other.