as far as I know, you can'y extend your visa after dec 2008, as u specified that that's when it expires right.

BUT, u can extend ur I-20 for another year or for as long as you need to complete ur education. Until then, that is, after dec 2008 to whatever length of time ur I-20 is extended, u can legally stay in the US, but if u leave the US after that, u won't be allowed to enter.

If u want to go to Nepal, make sure u go before dec 2008 and come back before dec 2008.

To have ur I-20 extended, just go to ur international students office and ask them for extension around Nov 2008. REMEMBER, ur I-20 can't be extended after it expires. So, let them know a little bit before ur I-20 expires.

Take care

Prabhat