1) First of all, you actually need the screensavers, obviously. I found the Win95 screensavers here. The nicer Win98 "Plus!" screensavers require you to have access to either a machine running Win98 that has the CAB recovery files stored on it, or have a Win98 installation or backup CD. This was a stopper for me for a bit, until I remembered that my old Dell laptop that I now use only for travel, since its so old that its not a huge deal if it gets broken or lost, is running Win98. Sure enough, I found the files I needed in the CAB files in C:\Windows\win98. The full themes, including the screensavers, start in the Win98_50.cab file and go through the Win98_68.cab file. The screensavers themselves are mostly located in Win98_63.cab, but I think you may need some of the DLL libaries on Win98_52.cab-Win98_58.cab for them to work, as well. (note: I know this is what the Microsoft site says the files are located at, but in my system I found the SCRs in _69.cab and the DLLs in _61.cab through _64.cab, so YMMV on which CAB they're actually in on your system). Myself, I wanted everything related to the themes, so I just copied all the files in the CABS from _50 to _68 and put them in one ZIP file for transfer to my XP machine. WinZIP or other archiving software should be able to extract the files from the CABS files.
1a) You can try creating a "Themes" folder under C:/Windows/system32/ if you don't want to chance overriding some of the files in there, or just want to keep them separate, but I'm not certain Windows will recognize the screensavers if you do that. I'd recommend keeping them in their own directory, then if there's certain ones you want to use after testing them out, copy only the files for that screensaver over to the system32 folder, where Windows should be able to recognize it. I've tested this for Mystery.scr, and it does work, after following the next two steps as well.
2) You need to download the file "kidplusd.exe" located here on the Microsoft FTP server (hat tip to this site for the location). Unfortunately the setup.exe doesn't work on XP, so you need to deconstruct the self-extracting EXE file into its components. I didn't have luck getting WinZIP to do this, but 7-Zip was able to. Here are the directions for what to do (works with XP as well):
1) copy the "kidplusd.exe" file from the site above.
2) use Winzip to unzip "kidplusd.exe" into the c:\Winnt\system32 directory. The result will be 5 new files (setup.ini, demothm1.cab, setup.exe, setup.1st, and setup.tdf). Don't run the setup.exe file.
3) use Winzip to unzip the "demothm1.cab" file into the c:\Winnt\system32 directory.
4) Access your screensaver options by right clicking anywhere on your desktop and select properties. Then select the screensaver tab.
5) Select the "Wildlife 32" option.
6) You now have the underwater screensaver offered by Win95/98/2000 Plus on Winnt.
3) From here, an additional step you have to take if you want to use each separately as regular screensavers in XP:
In addition to the .scr and .dll file for each screen saver, you also need the following two files (from the Windows 95 Plus! Pack or Windows 98):I found the two .DLL files in my regular system32 directory in Win98.
The next problem is that they all show up in the screensavers menu as "WildLife 32" instead of their proper names such as "Mystery", so you must use Resource Hacker to open each .scr file and modify the name "Wildlife 32" found in String Table, 1, 1033 to it's proper name (Mystery, Nature, etc). Be sure to click the "Compile Script" button in order for your changes to be saved. Now save the file and copy everything to your system32 directory. They should now be in your Screen Savers list. Enjoy.
A little lengthy, but I have been able to get the screensavers to work under XP by doing this.