First of all, make sure your text boxes which contain the data are named differently than the data itself. If you created the form with a wizard, bound text boxes tend to have the same name as the data they house (which, incidentally, is VERY VERY VERY annoying, Microsoft!!). Therefore if you have a data field actually called "Field1", then the text box should NOT be named "Field1". So in design mode, rename the text boxes somthing different that the data field names. It is recommended practice to use prefixes on controls in any case, so using your examples, rename the text box that is bound to Field1 to "txtField1" and Field2 to "txtField2". Finally, name the text box that you want to house the field "New SMF" as "txtSMF". Spaces in controls or fieldnames, while allowed, really make things complicated at times.
Once you have your changes, in design mode select txtSMF. On the Format menu, click "Conditional Formatting..." selection. Since you are going to create an expression, under Condition 1, change "Field Value Is" to "Expression Is". Now, since you want the formatting to occur if the value of SMF is more than the value of Field1 and less than the value of Field2, type the following in the text box to the right of "Expression Is:"
txtSMF.Value > txtField1.Value AND txtSMF.Value < txtField2.Value
Now set up the format conditions you need if that expression is True.
For more imformation on Conditional Formatting, check out this
Tutorial.