I am currently out of blank DVD's so my question is: Can I burn the iso to a CD instead or does it have to be a DVD?
You can't burn Ubuntu 13.04, or 12.10 ISO to a CD without first modifying the ISO. It would only fit on a DVD, since the ISO file size is almost 800MB. What you can do is make a bootable USB flash drive.
You can burn the Ubuntu 12.04 ISO successfully to a CD, but the ISOs of Ubuntu 12.10 and later Ubuntu releases are too large for a CD, so you have to use a DVD instead or create a live USB Startup Disk. There are several ways to create an Ubuntu live USB Startup Disk; the easiest way to do it is by using the built-in Startup Disk Creator application.
Not directly answering your question but perhaps another approach for you (or someone who stumbles upon this) to consider:
Given that some distros are going to be too large for a simple cd:
If your machine can boot from pen drive, if you have access to a windows box - you can easily get many distros onto pen drive with LinuxLive USB Creator
A slightly more wordy approach if you dont have a win box: Install Ubuntu from USB Stick
It depends what release you are planning to install, if you're installing earlier versions than 12.10 then you can use a CD, however for releases 12.10 or later:
Ubuntu 12.10 will increase the maximum size of its disc image from 700MB to 800MB, thereby making it too big to fit onto traditional CD-R media.
The news came from Canonical’s Kate Stewart on the Ubuntu Mailing list, who
There is no longer a traditional CD sized image, DVD or alternate image, but rather a single 800MB Ubuntu image that can be used from USB or DVD.
Ubuntu Server remains unaffected by the switch.
And as such CD's aren't typically able to store over 700MB of data so if you're planning on installing releases after 12.04, you'll have to either go with the USB options as suggested in the other answers, or you're stuck with having to buy a DVD.
Source and more info the matter: OMG Ubuntu: The Ubuntu LiveCD is dead
Given that the ISO file is almost 800MB, you cannot use a regular CD-R. However there are CD-Rs that were prepared for overburning, that is—writing data outside the regular space that is usually being read. Such overburnt CDs might not work with every optical disk reader though, but will be able to store more data. You need a special CD-R too, one that follows the CD-R99 standard.
If you use Brasero, it should show you a message about turning overburning on when you try to burn such an image.
Note that since the introduction of DVDs, this is basically asking for troubles—not every cd reader will accept such a drive, error rate might be bigger etc.
That depends on the kind of blank CDs you have.
The most commonly used have a capacity of 700 MB, but you can also get blank CDs with a capacity of 800MB or 900 MB.
For the LTS-version 12.04 you need at least 700MB, but for the more recent version 13.04 Version you'll need at least 800MB.
The capacity of your black CD should be written on the CD and/or on the package.
When you are out of DVDs you can also use an USB flash drive, which might be the easiest solution.
In ubuntu you can use the the tool usb-creator-gtk for that and on windows i recommend: http://www.linuxliveusb.com/
No, I have tried it two days ago. You will need a DVD. Anyway, a computer that has only a CD-ROM and not a DVD-ROM is probably too old for Ubuntu 13.04 and it will be very slugish unless you change the unity to some faster gui. On my old HP notebook (at least 4 years old) with 1GB RAM and 2GHZ CPU it's not very fast. And sometimes I am unable to do anything for 10-20 seconds or more seconds when I do something like updating and playing youtube video at the same time.
Newer builds of Ubuntu will no longer fit on a CD as Ubuntu decided to include more "space" for its developers to include more packages (Programs/apps) in the image as previous builds required for a stripped down build for CD and a bigger build for DVD. The change allows developers to have to only maintain one image and reduce testing. If your computer only has a CD drive, why not try using an USB or a DVD drive instead? Also, it is important to note that unless your computer is your own recent DIY build that didn't use a DVD drive to save costs, most older computers that don't even have a DVD drive should be too slow to even handle Ubuntu 13.04, and it may be better to use an older LTS image that can fit on a CD.
If you're able to provide a network connection to the installation target, you can use the Minimal CD that is only 30MB large. Of course, the installer has to download everything later so this may not be appropriate for your needs.
Another Option is to burn the 13.04 netboot installer to a CD and then install via internet or from a local network location: http://cdimage.ubuntu.com/netboot/13.04/
12.04 was the last Ubuntu release to be made available with an iso that would fit on a CD.