pspell/aspell extension

I am configuring my web Forum, and while i was trying to turn on the spell checker, I get the following message;

Spellchecker (This feature can not be turned on until your host installs the pspell/aspell extension!)

I tried to check on google, but i wasn't sure. So I said that i will ask u guys since u already have the experience.
If u can link me to some webpages that offers free downloads of the extension that will be really great.

I am hosting my web under my college, it will be more helpful if link me to some tutorial of how installing the extension.

Thanks allot.