Firstly - if the games worked in win98 try going to the .exe file for each game, right click and select properties. One of the tabs gives a compatability option for pre WinXP programs. See if this works.
If all else fails and you want to go back to win98 you will need to see if the hard drive has been formatted using the normal Windows File System in which case no problem. If it has been formatted to NTFS then the matter is a little harder.