Thanks for help. I actually didn't check forum posts, as I didn't get email notifications about other replies (must check settings for that in my profile), but I've managed to fix this by giving "min-height: 987px" in my css. I see Paul suggested almost same thing with "height: 100%", so thanks for that Paul.
@ Lemon Juice: I wouldn't like to use js, as some users might have disabled js... not many, but some might have. I will look at that today or tomorrow. Thanks.
I would also like to say that I like this forum a lot, especially you guys who are active in "CSS & Page Layout" section. You are always ready to help out and are also capable to help - I will definitely stick to sitepoint forum