Hi there,
I cannot install flash drive (USB) in Windows'98, is simply cannot detect it every time I connect a flash to my PC. Can suggest how to use a flash with Windows'98?
Thank you all in advance.

Win98 does not have the ability to automatically recognize most flash drives (like XP and Vista does). This is because Win98 does not inherently have a catalog of drivers for that type of device. So, the two things I can recommend are that you first go directly to the manufacturer's website and see if they have a driver that is compatible with win 98 and, second, if they don't, you can try this website which claims to have a few "generic" driver downloads that may work for some usb flash drives (see the download links near the bottom of the page): Windows 98 USB Mass Storage Device Drivers

I do appreciate your suggestions, thank you a lot.:)

You can find more information at this article on USB for older operating systems, including a link to a driver and a Microsoft article discussing the issue.