I had had some problems launching pear too some time ago. I've used the portable version of xampp for/at windows xp.
portable version of xampp means: I downloaded the zip file, extracted it to the root of a partition and started xampp without to start initially setup.bat.
Xampp and its components (e.g. Apache, Mysql, PHP etc worked fine) but not pear at the commandline, so I made some investigations in this issue.
if you don't launch the setup.bat of xampp at the install process, in every importend configuration files are the absolute path uncompleted. In fact, the leadinding drive letter of the partition in all paths are missing.
for instance: a part of the pear.ini file:
... s:12:"download_dir";s:22:"G:\xampp\pear\download";s:8:"test_dir";s:25:"G:\xampp\htdocs\pear\test";s:8:"data_dir";s:18:"G:\xampp\pear\data" ..."
example broken paths in pear.ini before:
The main components of xampp works very well with this restriction, pear does not.
I'm unsure, but I think, the the php-cli.exe, which uses broken paths from the C:\xampp\php\php.ini also doesn't work with broken paths (try C:\xampp\php>php -v I guess, it will fail).
This is, if I'm right, an restriction to the portable xampp at windows. You can't use pear with the poor unpacked xampp.
You have to configure xampp with absolute and full paths, to use pear. So you lost the ability, to use your xampp at a transportable Drive (Stick/ Hdd) at different windows systems.
Correct me, if what I wrote is false. But this was the only way for me to run pear. There is also a german discussion about the problem at :
( Bei der Beschreibung der Konfigurationsdateien sind mir dort allerdings in der Eile des Posts Fehler unterlaufen. Es sind in diesem Fall nur die Konfigurationsdateien \xampp\php\php.ini und \xampp\php\pear.ini relevant, um pear auf der Kommandozeile zum laufen zu kriegen.)