everytime I install a plugin i get an "allowed memory size axhausted" error

Here are four ways to increase PHP’s memory allocation:

1. If you’re using WordPress 2.9.2 or lower, try adding define('WP_MEMORY_LIMIT', '256M'); to your wp-config.php file. If you’re using WordPress 3.0 or higher, WordPress automatically does this for a variety of tasks, so there’s really no reason to try it in this case.

2. If you can edit or override the system php.ini file, increase the memory limit. For example, memory_limit = 256M

3. If you cannot edit or override the system php.ini file, add php_value memory_limit 256M to your .htaccess file.

4. If neither of these work, it’s time to ask your hosting provider to temporarily increase PHP’s memory allocation on your account. Keep in mind that most decent hosting providers allocate 32 MB to PHP under each account, and most decent hosting providers allow users to temporarily increase the memory allocation. If your hosting provider won’t accommodate you, perhaps it’s time to find a new hosting provider.

i am using wordpress 3.0.1

i’ve used your #1 sugggestion and added that line to my wp-config.php files. and that worked perfectly, thank you very much, you have helped me a great deal!

You’re welcome!