WASHINGTON, July 13: For some computer users, the reality of Windows 98 is turning out to be far less than the promise.Microsoft's latest operating system just recently hit store shelves around the world, but already upgrade horror stories, bugs, and incompatibilities are surfacing by the dozen. One of the features of Windows 98 that Microsoft has touted heavily is an improved setup routine. Some users, though, have found setting up Windows 98 anything but a pleasant experience.As a result, several major PC manufacturers including Compaq, Toshiba, and Dell have issued formal warnings. The upgrade, say the manufacturers, may cause conflicts and problems with some of their models.A statement from Dell Computer Corp. warns customers that the new features in Windows 98 will require a new set of system drivers in order for the operating system to function properly, and warns owners of its latitude series of notebook computers that in some cases, an update to your system bios may also berequired.Likewise, Compaq Computer Corp., the world's second-largest PC maker, has posted on its web site notices about a host of conflicts that arise when Windows 98 is installed on some of its models. The company's Windows 98 site, at Compaq.Com/athome/win98, details problems such as no CD-ROM support in DOS mode for its popular line of PCs, among other issues. And notebook maker Toshiba has also posted a warning on its web site telling users that a new setup chip, or bios, will be required on certain recently released portables in order for them to be compatible with Windows 98."I was afraid this was going to happen," said Dennis O'Keefe, a Maryland-based computer consultant for a large technology firm, of the latest Windows release. "I always wait for a couple of months before upgrading to see what the reaction will be."Millions of PC users, though, have not been so circumspect. Having heard from Microsoft and read in the computer press that Windows 98 was, in effect, a polished, lessbuggy version of Windows 95, millions of PC users justifiably felt it was safe to go out and buy the programme right away.So far, research indicates that Windows 98 sales have easily kept up with the rapid rate at which Windows 95 was snapped up by the computer community. In the United States alone, sales of the operating system reached well over half a million copies just one week after the program hit store shelves.But some of those looking for a hassle-free upgrade are clearly being disappointed. The complaints reported on Internet newsgroups and support areas range from applications not working properly to network cards not being recognized to Windows registry corruption and faulty plug-and-play card recognition.Roger Lanctot, director of research at Virginia-based PC Data, is among those following the public acceptance of Windows 98. Although Lanctot reports that he has not heard of any copies of the operating system being returned to stores, he has heard of various installation woes.