Install Ubuntu first...IF u have any problems then we'll be glad to help.
But relax....u likely won't have any problems. One more thing: Ubuntu does NOT detect my serial mouse (and neither does Fedora etc.) but its VERY EASY to make it work. Let us know if u have problems. Btw
www.ubuntuforums.org have a special subforum "Absolute Beginner Talk" for newbies. Check that out too.
Once Ubuntu is installed, u'll be given an option when ur PC boots whether u want to go into Windows or Ubuntu.
Hope u enjoy Ubuntu!