Login module in Website

Question

Hi,
i m developing a website (m a fresher)
i hv to done login lodule for admin part... and doing it without login controls

hv 2 probs...
1.
i hv done it like login, change password, forget password, update emailid etc.. bt the prob is in session

session expires autometically ... before its default time that is 20 mints
i hv to login again after few minutes without logging out

i want that session remains in exists till user logouts or browser windows closed

2. after logout he/she wont b able to see secured pages... wat to do for this...
why session expires?
pls tell me d solution of this prob... it wud be vry helpful

Thnxx