Help a newbie get Java installed

I know enough Unix to be dangerous, but not enough to get out of this one.  I got Ubuntu installed on my old PC, and it came up just fine.  Gnome is excellent!The partition editor says:/dev/sda1   ext3 format     35.70GiB total   2.04GiB used   33.65GiB free/dev/sda2   extended fmt    1.57GiB total        ---     used      ---         free> /dev/sda5 linux swap fmt  1.57GiB total       ---     used      ---         freeSo it looks like I have 33.65 free space.  I downloaded Java 6 SDK, but when I try to run it, it says "You will need at least 254104 kBytes of Disk Free.  Please free up the required Disk Space and try again."Last time I checked, 254MB fits nicely in 33.65GiB.  Huh?So in a shell window, I ran df -h and get:Filesystem            Size  Used Avail Use% Mounted ontmpfs                 316M   17M  299M   6% /lib/modules/2.6.24-19-generic/volatiletmpfs                 316M   17M  299M   6% /lib/modules/2.6.24-19-generic/volatilevarrun                316M  100K  315M   1% /var/runvarlock               316M  4.0K  316M   1% /var/lockudev                  316M   40K  316M   1% /devdevshm                316M   12K  316M   1% /dev/shmtmpfs                 316M   24K  316M   1% /tmpgvfs-fuse-daemon      316M  186M  130M  59% /home/ubuntu/.gvfsSo it looks like there's not more than 316MB free.  Can you help me understand what I'm seeing here?  I think perhaps that large drive is not mounted, but that's beyond my Unix skills.Help a noob?