You have to use ipsadmin ...
ipsadmin change domain name xml
In that look for the attribute
<iwt:Att name="iwtDesktop-allProviders"
userConfigurable="true"
>
<Val>iwtTabProvider|com.iplanet.portalserver.providers. tab.TabProvider</Val>
</iwt:Att>
that contains all the providers in the available provider list
add your provider name to your existing list of providers .
The above samples shows the format of a provider that was added ..
Also take a look at the threaded discussion below ..
http://softwareforum.sun.com/servlet/ProcessRequest?RHIVEID=181&RPAGEID=137 &HOID=50B5000000050000009B3D0000&HTHREAD=000015771000015772000015774& ;UCATEGORY_0=_8_&UCATEGORY_S=0
HTH ..