While installing Ubuntu it got about 80% done and I got an error,
Error executing script Dpkg::Post Invoke 'if[-d /var/lib/update-notifier] then touch /var/lib/update-notifier/ dpkg-run-stamp ; fi
E:Subprocess returned an error. Now it wont boot. I selected continue install and it appeared to do that, but never got the remove cd and restart message, so it must have blew up somewhere.
Would I be safe just trying to reinstall it or is it likely I would get the same error?

Try reinstalling, before that do a media check to ensure you have good CD/DVD.

It would be safe but just safe isn't necessarily useful.

As suggested, check the integrity of your cd if you still have it on your hard drive:
https://help.ubuntu.com/community/HowToMD5SUM

did you format you harddisk before install . try formating harddisk
.

do not just retry it. it takes really long time

just reburning Ubuntu cd with NICE CD/DVD

If you do this,

then retry install.

Anybody know what that error actually means?

Well I decided to start completely over. Deleted all the new partitions, restored windows, and in short started completely fresh. Bought a book on Ubuntu and read the installing part carefully, especially the parts on partitions. Reinstalled perfectly, no problems at all. Did all the updates, enabled Nvida drivers and everything is working well, including WinXP.
This isnt a problem but just a question, I noticed that during the update process the Linux kernel was updated, now Grub is showing an option to boot the original kernel and the new one, is that normal? I mean after numerous kernel updates are there going to be like 5 options for various kernels on Grub?

Yes, that's normal. Once you're sure everything is OK with the new kernel, you can delete the old kernel entries from /boot/grub/menu.lst.

I believe that GRUB records only the current kernel and the previous one. Anything older automaticallly gets deleted. You can actually control the number of kernels that it should keep by editing /boot/grub/menu.lst.