Re: System Switch-Windows & Ubuntu
If your e-mail is IMAP then you can open an e-mail reader in Ubuntu. Anything you do in your Linux e-mail client will be synchronized with your server and will be properly updated in your Windows client the moment you open it (and vice versa).
But I understand your issue and e-mail is just one example. If your HW is powerful enough, then what you are looking for is a technology called Virtual Machines (VM). There are many VMs around and some of them have their cores already built in to the Linux kernel. Two such are KVM and Xen, but they are rather involved and not very beginner-friendly. A better choice for beginners is either VirtualBox or VMWare. Explanation of a VM is here, which in turn contains a link to a very informative Wikipedia article.
Newb: How far must I jump to clear the ledge halfway down?
Guru: It's bad to jump off cliffs. Let's look at better options.
Newb: Stop harping about "best practices" and just let me jump.