Wallpapers are simple bitmaps so just open up the .CAB files with any CABVIEWER (see google.com) and copy them to your machine.
The screensavers are best forgotten about.
I have a new system with windows XP Pro and did not install screensavers and wallpaper from old computer. Is there a way to install these from my old 98 disk or does Microsoft have some sort of block to prevent doing it? Thanks