This isn't actually a "relationship" problem. It's a value list problem.
Open Manage Value List select your value list, and edit it. This should be a "Use values from field" value list. If not, select that option. In the next dialog you see, you get two boxes for "field 1" and "field 2". You can select the ID number for field 1, but then can select a name field for field 2. If you have a first name and last name field, you can define a calculation field that combines them and then select this calculation field for field 2. Now your value list will list both ID numbers and their names. Thus, you can select an employee by name, but the value list enters the ID number.
There is an option you can select to hide the ID numbers so that only names are displayed in the value list. Do not select this option unless you also take steps to make sure that the employee's full name is unique. Otherwise, cases where you get two employees named "john smith" for example, only one will be listed in your value list when this option is specified.
This is the simplest way to do this. It has some built in limitations that make it better suited for fairly small lists of values. There are a number of more advanced techniques that can be used that make working with large value lists easier to work with.
Always so simple! Thanks Phil!