Have you tried using ndiswrapper, its an option when you say ro configure a adsl connection. You will need the cd for the modem and take the .sys and int files off there. I cant give you a step by step or anything as Im using a router, but there is no doubt a walk thought in the wiki section of this site. Or somewhere on the web
Ndiswrapper should do the trick.
Failing that you could buy a router (i know its not an ideal solution), there more secure and far easier to set up then having to fiddle with device drivers and everything.
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edit heres alink with a walk through, it uses suse but it should be appicable to mandriva
http://www.lack-of.org.uk/viewarticle.php?article=114