Find a computer running windows 95
Copy the following files to a removable disk (USB stick, CD-R etc.)
C:\WINDOWS\EXPLORER.EXE
C:\WINDOWS\SYSTEM\SHELL32.DLL
C:\WINDOWS\SYSTEM\COMDLG32.DLL
Go to your machine running Windows 98
Back up the following files
C:\WINDOWS\EXPLORER.EXE
C:\WINDOWS\SYSTEM\SHELL32.DLL
C:\WINDOWS\SYSTEM\COMDLG32.DLL
Place the Windows 95 files in a directory (we'll just call the directory "95")
Go to shut down menu and select "restart in dos mode"
Type the following at the DOS prompt
COPY C:\95\EXPLORER.EXE C:\WINDOWS
COPY C:\95\SHELL32.DLL C:\WINDOWS\SYSTEM
COPY C:\95\COMDLG32.DLL C:\WINDOWS\SYSTEM
DOS will ask you if you want to over write the files, hit "y" every time.
type "exit" and windows will restart.
What this does is load the old fashioned Windows explorer which doesn't have all the "Web Integrated" crap that slows Windows down a lot. Please note however that some features may be disabled because of this. On one of my machines, I lost the drag and drop feature from doing this.
Please also note that I cannot be responsible for whatever what happens.
I'm sure there's an easier method to this, but this is how I did it.