Under Windows, how big does your HD appear to be? If it's only 40g then that means that there's another 40gb partition floating around there. If it shows 80gb, then it is likely that the whole disc was used by Windows and this would help confirm the fact that the Kubuntu installer also only sees the whole 80gb partition meaning your original Linux install is probably gone.
It's been a while since I installed Windows. If I'm not mistaken, the Windows installer will not recognize a preexisting ext3 partiton ( from your original Linux install) and so when you re-installed Windows you should have been given a 40gb part to install it on. Is it possible that you inadvertently selected the entire disc upon which to install Windows?
Not that familiar with your version of Kubuntu but if it is a Live version, you should be able to run it (without installing) and check the partitions under "places" .
FYI Unless you did something out of the ordinary, Linux automatically partitions any REMAINING free space (e.g. the 40gb space not used by Windows) into three partitions - a root part for the OS, a swap, and the rest for your home folder...so if you reinstall the Linux OS it won't touch your Linux home folder unless you tell it to. It will only rewrite the OS or (root /) partition and your Linux home folder will remain intact.
hope this helps
Edited by Trio3b, 27 July 2008 - 11:03 PM.