Why did you download a new version? You already had 3.0 which was the minimum required version (>=3.0 means equals 3.0 or higher). Did 3.0 not work in some way? If it worked fine, why not obey the 'dont fix whats not broken' rule.
To fix yum.
Download a copy of yum, for fedora, from the fedora website (or a mirror).
Install it by doing.
rpm -ivh yum-xxxx.rpm
If that fails, then find out the version of yum installed.
Now erase all of the rpms that show up that are yum or yum-devel or yum-xxx.src.rpm.
rpm -e somepackagename.rpm
Now try and install the copy of yum you downloaded.
PS. A small hint. If you dont have the internet at home, but have access at school, work, etc, and assuming you have no download limits. Download all the updates for your fedora version and burn them to a couple of dvd's. Then when you get home, you can copy the contents to your hard drive and with a little hack, make yum work locally.