I split my 200gb hard drive for the two OS's and they both boot fine.
When you "split" the hard drive, how much space did you allot toward the partition (or, as you've termed it, the "split") that you installed Ubuntu onto? Perhaps the size of the partition you created for Ubuntu simply wasn't big enough.
The / directory is the root directory. All other directories follow from this root directory (including media drives such as usb sticks, or cdrom drives, which are usually mounted in /media or /mnt directories.)
Enter the command "df" in your terminal (or console) and see what it says. This will tell you how much space is being used, and is available, for your Linux partition. If your Windows partition (aka drive) is also mounted, then this command will also tell you how much space is being used, and is available, for your Windows partition (I'm guessing that most of the "60+gbs" you refer to is in the Windows partition).
Assuming this is the case, you could increase your Linux partition with tool called GParted, available for install with Synaptic (or, on the command line, "sudo apt-get install gparted"). You could temporarily remove a large application like OpenOffice.org to make room for GParted (and then reinstall OpenOffice.org later). Or you could get the GParted LiveCD from http://gparted.sourceforge.net
via your Windows computer, and then use this to resize the partition.