Is your school account your primary email? -- You can set your outgoing email to appear to be from any email address you whic. In which case you can forget about your
account and only use your existing email.
You are likely trying to set up POP polling. I would just forward your email FROM your school account directly to the blackberry address. Then go from there.
Alternatively you can set up the blackebrry server to check your school's email at 15 minute intervals by programing your account details. If you don't have the server info, you will want to call your school's IT help desk (they definitely have one) and get them to give you the server details and type of server- ie: imap/pop/etc.