Hi Kanchhu !

OPT extension for STEM degree holder for 17 month is different from the cap-gap rule. Since u already got h1b receipt, you have to follow the following steps.

1. Submit a copy of ur h1b receipt and employment offer letter(if u have any) to DSO in your school and he will issue a new i-20 with opt extension till Sept 30th, 2008.

2. Make sure if the USCIS denys, revokes or rejects ur h1b, then ur OPT extension will be terminated 10 days after such type of notice and your 60 days grace period will be started.