I have two problems actually:

I recently tried to install kubuntu 5.10. The first installation process was smooth, but after the reboot when the second installation process starts, it fails at something like /lib/java and returns me at the terminal. I am not able to complete the installation process nor get the GUI. The system hangs at the root prompt. I tried the xserver commands, but it crashes. How can i complete the process or at least get the gui ?

I have windows 98se in one of my partitions and when i try to install fedora core 3 the process starts but crashes at the bug:
Assertion (heads > 0) at disk_dos.c:485 in function probe_partition_for_geom() failed.
Assertion (sectors <= 63) at disk_dos.c:490 in function probe_partition_for_geom() failed.
As suggested by various other posts, I tried the fdisk command to know the disk geometry, but as I don't have the rescue cd I get the message: Can't load the kernel image. i need some program to tell me my disk geometry, which I can use at boot. Example: linux hda=14593,255,63.

I am at fix and have googled for answers, but no luck. Any help in this regard will be appreciated.

I recently ran afoul of the limited functionality of Ubuntu's parted [ partitioning tool ]
what has happened is that Kubuntu has built partitions that are actually corrupted, thereby making them inaccessible from other distros.

The easiest way to fix this, redo the entire installation.
the other way, use the console prompt and run aptitude ( if it is there ), then make sure the gui is installed.

From what I understand, I think this is a partitioning proble. (a) could be because of some bad sectors.

You can, if you are up to it, try to create the partitions with some other software. Try fdisk maybe? But needless to say, you must try to install ubuntu again and hope that the problem is sorted itself.