i am using php in order to validate a form where users register. please help me to solve the following validations.

1. name can have spaces. ex= john smith
presently the validation i am using is if( $fname == "" || !eregi("^[a-zA-Z_]+$", $fname) )
i need the syntax which would accept a-zA-Z WITH A SPACE IN BETWEEN NAMES ex= john smith

2. text can have spaces and special characters ex= ref 100/abcd
presently the validation i am using is if( $depositnumber == "" || !eregi("^[a-zA-Z0-9_]+$", $depositnumber) )
i need the syntax which would accept a-zA-Z0-9 WITH A SPACE IN BETWEEN AND SPECIAL CHARACTERS ex= ref 100/abcd

3. spaces in numbers. ex= 123 4567
presently the validation i am using is if( $phonenumber == "" || !eregi("^[0-9]+$", $phonenumber) )
i need the syntax which would accept 0-9 WITH A SPACE IN BETWEEN
ex= 123 4567

4. in case of [a-zA-Z0-9_] if i remove the "_" after 9 will it have a negative impact or is this a syntax due to which i
should i leave the "_" as part of [a-zA-Z0-9_]

5. using stripslashes() function
due to the above validation there is no way a user can enter special characters which could lead to sql injection. inspite of
this should i still use stripslashes to be on the safe side.

please provide the exact syntax for the above validations to works as specified for different scenarios.

thanks.