after doing "expert" install, can't create new partitions

If this "bug" should have gone to a mailing list instead, my apologies. Please
let me know.

I have just installed ubuntu by using "expert" at the "boot:" prompt and now I
need to create some more partitions (which I wish now that I made during the
installation) and I have used fdisk several times on other distros and created
partitions, put a filesystemm on the partition, created mount point directories,
mounted the partitions on the directories and added the partitions to fstab.

At the $ prompt (for a non-root user), I ran: su - and put in the root
password and ran fdisk and tried to create the partitions and I also used: sudo
 fdisk /dev/hda and neither of these worked. However, there may be something
wrong with my setup. Should the name of the non-root user that I created during
the installation be in the /etc/sudoers file? I also can't run administrator
gui utilities (such as to create users and groups) from the desktop. When I get
asked for the password and I put in the password of the root user or the
password of the non-root user, neither provides access to the administrator gui
utilities.

I have 3 primary partitions and an Extended with 3 logical partitions and about
80 GB of available disk space. I run: fdisk /dev/hda and type n to create a
new partition and the default starting cyl is 4501 (and the range is 4501-4502)
and I press Enter and at the prompt for the size, I type in: +50M and press
Enter and I get an "out of range" error message. All of this can be seen below.

Do I need to run fdisk with sudo? Can I run: su - and then run fdisk?
Does X need to be shut down to run fdisk?
Do I need to be in runlevel 1 (which I tried) to be able to run fdisk?
With 3 primary and one Extended, should I not be able to create more than three
logical partitions in the extended partition?
Is the partition location of the swap partition a problem?

Basically, why can't I create partitions on my other 80 GB of disk space? Any
help would be GREATLY appreciated. Thanks in advance. Clyde

There are 14946 cylinders on the disk, the last first avail cyl is 4501 and the
last is 4502 (as shown below).

The fdisk "session" is shown below.

The number of cylinders for this disk is set to 14946.
There is nothing wrong with that, but this is larger than 1024,
and could in certain setups cause problems with:
1) software that runs at boot time (e.g., old versions of LILO)
2) booting and partitioning software from other OSs
   (e.g., DOS FDISK, OS/2 FDISK)

Command (m for help): p

Disk /dev/hda: 122.9 GB, 122942324736 bytes
255 heads, 63 sectors/track, 14946 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

   Device Boot Start End Blocks Id System
/dev/hda1 1 61 489951 83 Linux
/dev/hda2 62 547 3903795 83 Linux
/dev/hda3 548 1398 6835657+ 83 Linux
/dev/hda4 1399 4502 24932880 5 Extended
/dev/hda5 1399 2006 4883728+ 83 Linux
/dev/hda6 2007 4438 19535008+ 83 Linux
/dev/hda7 4439 4500 497983+ 82 Linux swap / Solaris

Command (m for help): n
First cylinder (4501-4502, default 4501):
Using default value 4501
Last cylinder or +size or +sizeM or +sizeK (4501-4502, default 4502): +50M
Value out of range.
Last cylinder or +size or +sizeM or +sizeK (4501-4502, default 4502):

The current contents of fstab and the output of: fdisk -l /dev/hda are shown
below.

# /etc/fstab: static file system information.
#
# <file system> <mount point> <type> <options> <dump> <pass>
proc /proc proc defaults 0 0
/dev/hda2 / ext3 defaults,errors=remount-ro 0 1
/dev/hda1 /boot ext3 defaults 0 2
/dev/hda6 /home ext3 defaults 0 2
/dev/hda3 /usr ext3 defaults 0 2
/dev/hda5 /var ext3 defaults 0 2
/dev/hda7 none swap sw 0 0
/dev/hdc /media/cdrom0 udf,iso9660 ro,user,noauto 0 0
/dev/fd0 /media/floppy0 auto rw,user,noauto 0 0

The current partitions are shown below:

root@lancom77:~ # fdisk -l /dev/hda

Disk /dev/hda: 122.9 GB, 122942324736 bytes
255 heads, 63 sectors/track, 14946 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

   Device Boot Start End Blocks Id System
/dev/hda1 1 61 489951 83 Linux
/dev/hda2 62 547 3903795 83 Linux
/dev/hda3 548 1398 6835657+ 83 Linux
/dev/hda4 1399 4502 24932880 5 Extended
/dev/hda5 1399 2006 4883728+ 83 Linux
/dev/hda6 2007 4438 19535008+ 83 Linux
/dev/hda7 4439 4500 497983+ 82 Linux swap / Solaris