can i run ubuntu on my pc without installing it, but still run windows later without any changes?

The Live Cd does not modify your harddrive at all unless you tell it to install ubuntu.
The downside to this is that any changes you make in ubuntu will be lost when you close the live cd.

When you boot into the live enviroment, ubuntu only utilizes your RAM and cd drive. Your windows installation will remain untouched until you ask it to install.

There is a second option. You can run a virtual machine such as vmware, and install ubuntu. It will be like running ubuntu in a window without actually installing it next to your xp installation. In this way, you will be able to save things.

can i run ubuntu 9.04 from the cd as my primary operating system on a windows computer without losing the info stored[saved] on the computer,such as factory operating info.

Well you can either install ubuntu and dual boot which would be most sensible if you have the harddrive space. It wont touch your windows install at all and at boot you are given an option of which system you want to boot into.

The other option which your question seems to be pointing towards is: can you run the live cd at boot every single time. This is also a yes but realize everytime you turn off the computer all changes made in ubuntu are lost as they are not saved. Also the boot times for a live cd are little longer as are loading many applications. Id advise you to just go with the dual boot option. You can even install ubuntu as an "application" and if you dont like it just uninstall it.