So, I updated from FC6 to 7 (using the DVD) and while I was trying to fix the video card driver I started getting "cannot open/read repomd.xml repository: fedora" errors. After that the only way I got yum to work was to disable/remove fedora.repo and fedora-updates.repo, but I think that might cause me problems later.

The (previously) enabled bit of fedora.repo had looked like this:

Would someone suggest what I might need to change, please? (Also, it might help me if someone could provide an example list of enabled repositories for F7)

You can figure this out and fix the issue by yourself, starting with a copy of the fedora-release-7-3.noarch.rpm in some directory type:

rpm2cpio < fedora-release-7-3.noarch.rpm > fc7.cpio
cpio -i -d < yum.cpio

Then have a look in the resulting yum.repos.d subdirectory at the repo files, but to save you a bit of time;

From the fedora.repo file:
[fedora]
name=Fedora $releasever - $basearch
#baseurl=http://download.fedora.redhat.com/pub/fedora/linux/releases/$releasever/Everything/$basearch/os/
mirrorlist=http://mirrors.fedoraproject.org/mirrorlist?repo=fedora-$releasever&arch=$basearch
enabled=1
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-fedora file:///etc/pki/rpm-gpg/RPM-GPG-KEY

And from the fedora-updates.repo file:
[updates]
name=Fedora $releasever - $basearch - Updates
#baseurl=http://download.fedora.redhat.com/pub/fedora/linux/updates/$releasever/$basearch/
mirrorlist=http://mirrors.fedoraproject.org/mirrorlist?repo=updates-released-f$releasever&arch=$basearch
enabled=1
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-fedora

You can (and should) copy all the repo files to the /etc/yun.repos.d directory and remove the older fedora related repo files.

Thanks! I didn't know about rpm2cpio.

I actually got it working a minute ago by wiping out everything in /etc/yum.repos.d/ and then erasing the fedora-release-6-4 and reinstalling fedora-release-7-3.