To delete the whole thing do this:
Boot with your ubuntu cd or USB stick.
When it's finished booting go to terminal 1.
In Linux this is done by typing ctrl+alt+F1 (function key F1)
Then type
Check what fdisk produces.
If you see /dev/sdax and /dev/sdbx you're ok.
Then
you'll see something like this
fdisk /dev/sdb
Command (m for help):
Now type m and you'll get this
Command (m for help): m
Command action
a toggle a bootable flag
b edit bsd disklabel
c toggle the dos compatibility flag
d delete a partition
l list known partition types
m print this menu
n add a new partition
o create a new empty DOS partition table
p print the partition table
q quit without saving changes
s create a new empty Sun disklabel
t change a partition's system id
u change display/entry units
v verify the partition table
w write table to disk and exit
x extra functionality (experts only)
Command (m for help):
Now type d.
It will ask you which number to delete.
If it shows more than one partition start deleting the highest number first.
Then type p.
It will show you if there's anything left.
When there are no more partitions left do n.
This will make a new partition.
If you want to have just one partition make it a primary partition.
You will have then to hit Enter twice.
To finish type w.
That's it.
Of course the partition still needs to be formatted but that can be done by the ubuntu installer.
An alternative is just deleting all the partitions and then type w and let ubuntu do the rest.
Gerard.