Sales Process Query

 Hi All,

I want to make certain fields as mandatory when a particular sales stage is selcted, this I was able to do it via sales process.

The mandatory field B is a picklist and has several values...my requirement is

When sales stage is A, picklist value of field B should be 1
When sales stage is B, picklist value of field B should be 2
When sales stage is B, picklist value of field B should be 3

Note:The sales stage names are common across the application, can I use sales stage id to make sure that the validation or workflow is unique for this sales process alone? How can I retrieve the sales stage id?