Upgrade to PHP5, Experiencing several errors

PunBB 1.3.2
Operating system: Linux
PHP: 5.2.5
MySQL Standard 4.1.22

Awhile back I installed PunBB 1.3.2 while server was configured for PHP 4.4.8. Just modified .htaccess to enable PHP 5.2.5 which has resulted in several errors.

1) was not able to access extensions section through admin. I had to revert to PHP 4.4.8 and uninstall extensions then go back to PHP 5.2.5, reinstall the hotfixes and 'antispam' extension.

2) The CAPTCHA image is not displaying now after going back to PHP 5.2.5.  The URL for the CAPTCHA image is: http://scas.abuxton.com/PunBB1.3.2/exte … a1bedc080e

3) I'm getting errors on login page just under the password form field:
Warning: session_start() [function.session-start]: open(/tmp/sess_548b7bb78ac746950c65d3cbe22c4b80, O_RDWR) failed: Permission denied (13) in /home/.../public_html/PunBB1.3.2/login.php(433) : eval()'d code on line 13

ALSO, at the bottom of the login page

open(/tmp/sess_548b7bb78ac746950c65d3cbe22c4b80, O_RDWR) failed: Permission denied (13) in Unknown on line 0

Warning: Unknown: Failed to write session data (files). Please verify that the current setting of session.save_path is correct () in Unknown on line 0

Here are my PHP Session settings:
Directive    Local Value    Master Value
session.auto_start    Off    Off
session.bug_compat_42    On    On
session.bug_compat_warn    On    On
session.cache_expire    180    180
session.cache_limiter    nocache    nocache
session.cookie_domain    no value    no value
session.cookie_httponly    Off    Off
session.cookie_lifetime    0    0
session.cookie_path    /    /
session.cookie_secure    Off    Off
session.entropy_file    no value    no value
session.entropy_length    0    0
session.gc_divisor    100    100
session.gc_maxlifetime    1440    1440
session.gc_probability    1    1
session.hash_bits_per_character    4    4
session.hash_function    0    0
session.name    PHPSESSID    PHPSESSID
session.referer_check    no value    no value
session.save_handler    files    files
session.save_path    no value    no value
session.serialize_handler    php    php
session.use_cookies    On    On
session.use_only_cookies    Off    Off
session.use_trans_sid    0    0

Any Advice is greatly appreciated