Not only is that not possible, it makes no sense.
In SQL, and in Crystal, grouping occurs on DATA, not on parameters. Have you ever heard of someone writting a stored procedure which groups on a parameter passed? parameters aren't data, sql groups on data.
To further annoy you, Crystal built in the description to allow for display, but you can't reference it in code (annoys me anyway).
So create a formula to group on, such as:
if {table.field} = 1 then
"My first group"
else
if {table.field} = 2 then
"My Second group"
else
"N/A"
Make sure that the names will sort properly alphabetically, or you can group by whatever field is appropriate and use the above formula for display purposes.
-k