I was upgrading RedHat 7.0 (up-to-date patches installed) on my Pentium 
Pro 200MHz 176M of memory system (Intel PR440FX mother board)

Here is the list of problems that I ancountered:

1. Created biit disk form bet1 CD1
dd if=boot.img of=/dev/fd0
OK!

2. Booted the system using boot disk
OK!

3. Selected default on install screen "Enter"
Problem: It took very long time (2 Hours) to go trough hardware detection 
before I got Xserver instalation screen

4. Aborted and rebooted as in step 2.

5. Instead of selecting default I typed:
linux mem=176M
Problem: Same as in step 3.

6. Aborted and rebooted as in step 2.

7. Instead of selecting default I typed:
linux mem=128M
OK! It worked significantly faster.
It took only 2 Minutes to go trough hardware detection before I got 
Xserver instalation screen

8. Proceaded with instalation
OK!

9. Removed boot floppy and CD-ROM
10. Rebooted the server as requested on the screen
11. At boot prompt I selected linux from graphics screen
12. Server hanged
13. Rebooted
14. At boot prompt I selected linux-u from graphics screen
15. I was able to boot server and get to # prompt
16. Investigated the problem why it would not boot as linux
Problem: /boot/initrd-2.4.0-0.43.6.img and /boot/initrd-2.4.0-
0.43.6smp.img where not there. 
/etc/lilo.conf had only original information from 7.0
17. Tryed to create immage file:
cd /boot
mkinitrd initrd-2.4.0-0.43.6.img 2.4.0-0.43.6
Problem: System complains about all loopback devices being used.

System is in unusable state and prior version of the kernel is removed.

Suggestion:
Please provide mechanizm in instalation process to preserve prior version 
of the kernel during upgrade.