just install either vmware player or virtualbox in windows (both are free). then download the ubuntu iso and then fire up your VM program amd follow the "create VM" wizard sort of thing. when it asks you where to save the virtual disk, i hope you have a separate physical disk that windows isn't running off. running a guest and host off the same disk is pretty painful performance wise even if the rest of your spec is kick ass.
Sounds like it'll be pretty decent on the same disk, both going to be fairly idle most of the time.
If you were running production VM's you'd want a more elegant storage solution. Probably a separate storage controller.