Handling mulivalued selection of resource level custom field

Hi,

I have custom field called 'Skillset' which is referring to lookup ('Available skills')(ex. c , C++, Java, dot net, php etc.)

Requirement is:

I need to provide custom page to user so that he can select multiple skills from the customized form.

Using PSI i.e. asmx based web service I am able read projects, resource.

But I need help on how to handle multivalued selection of custom field through PSI.

Your help is appreciated !!

Thanks in advance

-Rohit