RADIUS client for Unix ?

Is it possible to use the RADIUS to authenticate Unix users ? (means, instead of using the local passwd file)
Our radius server, VASCO, is running on NT. If it is possible, I guess a RADIUS clients to my unix machines is needed (We are using AIX, HP-UX and Dec-Unix) do you know where can I get it ?
The radius supplier, VASCO, don’t have them
and I have search the Unix suppliers sites, but could not find any clients, I have also checked http://www.freeradius.org .