Windows Died, Ubuntu Install

My sister gave me her Dell Inspiron 1520 after her Windows install became corrupted and can't start and she can't find her repair disk. She's gotten everything off of the drive and she said I could have the computer. I want to put Ubuntu 11.04 on it, and I've got the CD, I just don't know if I should let Ubuntu do the whole disk or if I should pick where to install it, I don't know anything about deviding hard drive space, all I know is there are 4 different partitions according to Ubuntu, and I know Dell made the laptop like that and I don't want to erase anything except Windows. What would happen to the BIOS and stuff if I let Ubuntu install to the whole thing? I think Windows might have been on the second partition because that's the biggest one, but I don't know. Can anyone help me? Thanks. Ubuntu doesn't recognise Windows as a valid OS to be installed alongside it and it does not give that option, it just says Erase Disk or whatever the second option says and Something Else, then it asks do I want Ubuntu to have the whole disk or do I want to use the advanced tool that says 4 partitions to pick where to put it, so I guess that means Windows has been destroyed. I just want to replace Windows with Ubuntu. This will be my first install of an OS besides Windows.