you simply need the Senoa or Intersil prism drivers (which is the chipset on the WCF12 card) I can't post the link to the Intersil drivers as noted by Mr Dunn but i can however post the link to the Senao ones... I use these and they are better since they offer perfect compatibility with WM 2003. The built in Wi-Fi works with these drivers..
http://www.senao.com/service%20&%20s...inCENET400.zip
Should have researched before you got the ambicom card.. this was posted on here many times (i posted it 4 times now) so search next time
Oh and yeah, delete the link to the WLAN application and the app from program files using file explorer... (no need as it doesn't work) With Wi-Fi on all the time WM 2003 will alert you if there's any wi-fi near like it's shown on MS
NOTE
When you install the card it'll still say "Unrecognised card" blah blah... so type in the name "WLANNDS.DLL" (without the quotes and doesn't have to be all caps) So from then on whenever you install the card it'll know what driver to use (so that means you wont have to keep typing in the name each time)