The memory should display before entering the BIOS in the POST but if you enter into the BIOS usually with the delete key you may be able to scroll through and see the memory in there.
Just install something lke PC Wizard or CPU-Z. It will show you how much memory you have. System Information in Windows will tell you too.
Yup.
On windows 7 and Vista, right click "computer" from the start menu and choose properties. In XP, cick start and then run. Type in dxdiag and it'll say in there.