security - Site hacked - any ideas of what to do, where to look?

A site I host was recently hacked. The index page had the following code added to the bottom (just above the closing body tag):

Followed by...

Lots and lots of tags going to
spammy sites...

Our server has suphp installed, so I don't think it could've happened from another account. This account does have Wordpress installed, so that may be the problem.

Any tips on where to go from here?

Thanks!