UBB.Developers Forums Community Development Programming PHP and Server-side Scripting Strings

I would like to find part a string and then be able to delete it.
For example if i had the string
"This is a string"
I would like to delete the word "is"
HOw would i do this, and retani the rest of the string, so that i end up with "This a string"
This will need to be done for many different strings, so i cannot simply use strlen() functions to return a specific lenght of the string.