What class of PC are you using,
Safest bet 2.4.20_8-8.26a9-1.i386.rpm will work on all PCs
Pentium III, IV,Celeron 2.4.20_8-8.26a9-1.i686.
For instance i686 can run any of the other versions i586, i486, 1386.
An i586 can run i486,i386. Hope this clears it up some.
This last bit is just depending what your kernel would have been set-up for the i386 will work, the higher levels are just for faster PCs.
To be sure which one matches press Ctrl-Alt-F2
this will drop you to a Console and if you read along the top you should see which one matches your kernel for instance when I do this I get 2.4.20-18.9acpi on an i686
my kernel was compiled for an i686. Then once you get the information you will press Ctrl-Alt-F7
which will take you back to your GUI.
Hope this Helps