Are you sure you're putting this formula in the right place?
I'm using CR9. My Excel export dll (crxf_xls.dll) version is 9.2.1.686. This combination exports coloured borders to Excel okay.
But I don't think your version of Crystal or dll is the problem here. The symptoms you describe sound as if you've entered this in the Color/Border area, where you can select the colour of your border.
This drop down should point to yellow. You don't need to apply a condition here.
I haven't used v8 for quite some time, but I'm pretty sure that right at the top of the Border tab, under Line Style, you should have components for each side of the box. You need to enter the formula I gave you in Left/Right/Top/and Bottom.
Naith