How to resize vdi virtual hard drive of VirtuqlBox install

Here is my problem: I created an OS X Snow Leopard machine with VirtualBox (host is a windows 7 machine). I made the virtual hard drive dynamic, 20 gigs max. Installed the OS, updated to 10.6.8 (I wouldn't say no problems, but I got it to work). Now I would like to install Xcode 3, but it requires about 10 gigs of space, and it's a little bit more than I have. So I would like to increase the maximum size of my virtual hard drive, and that's where I'm encountering problems. I used the VBoxManage modifyhd --resize 100000 command line to increase the maximum size of the vdi to 40 gigs. That worked. Now I would like to resize the partition within the OS. I mounted a gparted live iso and booted on it. It sees the drive (dev/sda), but says the size is still 20 GB. The drive itself is split in 3 partitions: a FAT32 (label EFI) of 200 MB with a "boot" flag, then the OS X partition (file system HFS+), with a warning that says "unable to read the contents of this file system", and then 182 MB unallocated (graphics memory?). According to this site this is not what I should get. Can anyone help? Thanks.

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