The original version of Windows 98 does not support USB, you need 98SE to be able to connect USB devices. The fact that you have managed to view files, albeit one at a time using Windows Imaging, implies that you have 98SE. If you didn't have SE, you wouldn't have even got this far.
With the camera connected, you will probably find that you have another drive (such as, for example F
shown in "My Computer". This new drive, which is not present without having the camera tethered, will be the drive you need to access to get the files off the card. By clicking on this drive, you should be able to select all the files on the card (in whichever folder the camera has put them) and move them to your normal hard drive location. Once they are there, it should be possible to view them using the picture file browser software that came with your camera.
As Stephen has said, a stand-alone card reader is the way to go, they are very cheap, and well worth the money.
Regards,
Duncan