Is there a 10 gig limit on HD size?
No, as YouCanToo said, there is not. I have a 326GB partition on one 1TB drive a 318GB on another.
I've tried both LXDE and XFCE, both installs were with full reformat on 20 (18.7) gig HD, giving the full HD (no portions) to the OS.
Both only saw about 10 gigs. 
You must have at least one partition. You can only install to a partition, not to an unpartitioned drive. But if you only have one, that one partition should take up all of the space on the drive. Apparently it doesn't in your case.
Please open a terminal and post the output of the command
fdisk -l -u=cylinders
Some people would insist that you enter the command as root, but actually you don't have to. (The "-l" option is a lower case L.)
Well, actually you can install to the raw device (this is Linux after, all, and the user has a lot of control!

), but it really isn't a good idea, and has little benefit...
Some might be right...depends on how things are setup?
[jpaglia@gx620 Videos]$ fdisk -l
[jpaglia@gx620 Videos]$ fdisk -l -u=cylinders
[jpaglia@gx620 Videos]$

Oh, and no 10 GB limit here:
[jpaglia@grendel ~]$ df
Filesystem Size Used Avail Use% Mounted on
/dev/sda1 9.4G 7.9G 1.1G 88% /
/dev/sda6 218G 43G 175G 20% /mnt/oldhome
/dev/sdb1 1.4T 1.0T 375G 74% /home
[jpaglia@grendel ~]$
Yes that is a Terabyte partition (it's a bugger to backup

), and this install still needs to be updated from 2009...

When I finally get around to it, I figure
/dev/sda6 can become the new root, at 218G, and
/dev/sda1 will languish for a while as a backup...