I have a dual boot sys: Window 7 and Jolicloud.
If I delete Jolicloud in win7 can I reuse the 10gig partition for ubuntu remix
Thank you for clarifying the question. Yes you can.
Say you delete the partition in windows, the Installer will then give you the option to use the free space for Ubuntu. If you don't, the installer will also let you delete the partition.
Just put in an Ubuntu CD and give it a try! You will be warned before you commit to any changes, so you can make absolutely sure that you're happy with Ubuntu's changes to your hard drive before proceeding to install it.
10GB of space may be a bit small for Ubuntu. It should install no problem (it only needs around 2.6 gigabytes), but - if you can - consider allocating a bit more space.