If you are looking for drivers for the Sandisk USB stick drives, then you might be surprised to find that there are no drivers required on modern operating systems. If the USB stick is being plugged in and nothing is coming up, or it says unrecognized device.... there may be a fault in the USB stick. Try it in another computer to rule out a bad USB port too.
If you want to use a USB stick on Windows 98, there are Windows 98 USB Drivers.
There is a piece of software called SanDisk SecureAccess that allows you to secure files that are on the USB stick using encryption, which can be downloaded on the Sandisk website, or with the direct link below.
Beware of sites offering drivers for USB sticks, they are almost aways malware sites.