If you want to become the new lead maintainer of a package that is marked as unmaintained on the PEAR website, the following section will explain to you the necessary steps for this to happen.
The first thing is to inform the PEAR Quality Assurance mailing list about your intention. If you have not been involved in PEAR prior to that, it is a good idea to write a few words about you and your motivations.
The QA team will then state whether you can take over the package or not, eventually explaining why. You can then apply for an account for the PEAR website unless you already have one. The PEAR Group will have to grant this account, and afterwards the QA team will assign you as the new lead maintainer for the package.
If the sources of the package are kept in the PHP CVS repository, you will also need an account for this. You can sign up for it on the PHP website. Please mention in the purpose field of the request form that the PEAR QA team has told you to get an account, so that your request can be processed faster. CVS accounts are managed by the PHP Group, so PEAR unfortunately has only limited influence on this process.
Note: If you already have a CVS account for cvs.php.net, it is only necessary for you to get additional "karma" for the module where the package resides. You can request this karma by sending an email to the PEAR Group. (Please also mention in this mail that you have already talked to the QA team.)
If everything has worked out well, you should by now be the lead maintainer of the previously unmaintained package. If not, don't hesitate to ask the people on the QA mailing list for help.