I would suggest that before you do this you change the
volume name (using Windows Explorer) on the partition
you wish to delete to something oblivious (Example: DELME)
Then reboot verifying that you booted off of the partition you
wish to keep.
Then use 'Disk Management' on your Windows PC.
Right click on the My Computer icon,
then select the Manage option,
then in the Computer Management window
select Disk Management.
If you really do have two partitions then Disk Management
will show something like:
Disk 0, Basic, and the Total disk size followed by the
two partition blocks and each partitions size.
To delete a partition, right click on the partition you wish to
delete (DELME) and from the list of options you should see
the 'Delete partition' option. Most likely this would be the
second partition on your hard drive.
Keep in mind this is a one way trip and once deleted you
loose all data and that Windows installation.
You then may need to change the boot.ini to reflect
the fact that you now have only one Windows OS
to boot from.
If you have any questions about this procedure
please post back before you try something that
will end up leaving you PC unbootable.