Many people find that there is a particular set of drivers (not necessarily the NEWEST) that allow the use of Sparkling Water with Nvidia cards.
Go to the SIMHQ F/A-18 forum and check out the Graphics Faq.
There was just a report, however, that with the installation of Directx 9.0c the grid lines were back even though a driver set that worked with DX 9.0b was installed.
The sad fact is, that Windows XP causes MANY problems with F/A-18, though it will run with enough tweaking.