That link downloads the 32bit version. you should download the 64bit version; here:
it'll allow you to do both; try ubuntu and install it permanently if you want.
Don't worry about the size; this is the whole ubuntu ;)
...by the way this is the LTS (long-term support) version of ubuntu (12.04), there is a newer version of ubuntu (13.10) here:
but the idea is that ubuntu releases a new version often and therefore it stops supporting this version (13.10) whereas it'll continue to support 12.04 for a very long time
... also if you get the 13.10 version and then a new version is released and you want to update your ubuntu to the next version, you can upgrade it very easily from the software updater from inside ubuntu itself, one reboot and you have the newer version
I have 13.10 and I recommend it for you. It's much better and it's very easy to upgrade later. chose what suits you best ;)