What I would do is:
Download the latest drivers for your card:

http://www.realtek.com.tw/downloads/...&Software=True
They were recently updated.
Description Version Update Time File Size FTP(TW) FTP
(CN) FTP
(HK)
Auto installation program(support Win95/Win98/WinME/Win2K/WinXP) ver.5.05 4.51.5.05 2003/01/06


completely unistall the Realtek device.. From windows

Then shutdown the PC.
Then move the card from the current PCI slot in your PC.
Turn the PC on,
Reinstall the latest drivers. When you reinstall it, don't let XP do the hardware wizard, if you can stop it, then stop it. IF not, then tell the wizard to install the drivers from a specific location and choose the place where you unzipped the drivers from the downloaded driver site at the link I listed above.

Go into Hardware device list and check to see if wan mini port is still not installed.
If it is installed, problem solved.

If not, you have ruled out the drivers, the PCI slot, etc...

It could be an issue with your modem or OS.

If it is working fine, you can surf the internet, you're not getting any errors, it might be something you can live without fixing.

Keep us updated.
BB