Installed Ubuntu 11.10 on my Samsung RC418 laptop. It said it installed successfully but when it rebooted it defaulted to windows and it didn't give me the option to choose an OS.
Please help me since I'm a first time user.
If you have already installed Ubuntu, then you probably did not install the GRUB (GRand Unified Bootloader) correctly - which can happen on occasion.
To fix this:
During the installer, I'm assuming you used the advanced partition editor? (selected "something else") Run the installer again, this time making sure the "Disk for Bootloader installation" is set to your local hard drive (probably /dev/sda).