When using datasheet view to SQL server, you cannot use a lookup.
However what you can do is create a continues form, and then simply drop in a combo box and use the wizard (or by hand) build the drop down and lookup you require. From the users point of view, they not really be able to discern the difference between editing data in that continues form as opposed to a continues form.
So the continues form will be based on the ONE table. The combo box column will be a long Number, and the combo box will have a row source of the table that provides the list of choices (the lookup values).
So you can build a screen like this:
Note how in above we have a continues form, but also some buttons etc. So a continues form is more flexible then a datasheet, but this “multiple items” forms result in much the same user interface.
Note how the first column is a combo box. In fact as above shows, you can drop in near any kind of control into these continues forms. The combo box can/will display a text column of your choice, but “behind” the scenes the combo box will store the PK id of the value you choose from the combo box into a single column in your forms table.
The result and look and feel is the same as a lookup column in an Access datasheet.